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ELEMENTARY QUALITATIVE 
ANALYSIS OF THE METALS 
AND ACID RADICALS 

A LABORATORY MANUAL 


FREDERICK C. REEVE, E.E. 

It 

ACTING HEAD OF THE DEPARTMENT OF PHYSICS AND CHEMISTRY AT THE EAST 
SIDE HIGH SCHOOL, NEWARK, NEW JERSEY 



NEW YORK 

D. VAN NOSTRAND COMPANY 

Eight Warren Street 





Copyright, 1921 

By D. Van Nostrand Company 


< 

c c 


AUG 12 1921 


PUBLISHED IN THE UNITED STATES OF AMERICA 


©CI.A617930 


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PREFACE. 


This book is the outcome of seven years of experience by 
the author in teaching Elementary Qualitative Analysis. 
In order to make the work a success it was necessary to 
prepare special outlines of the subject. The experiment 
has been a very decided success. Pupils were found to 
become deeply interested in the subject and found advanced 
work comparatively easy. It seemed desirable to extend 
the usefulness of the outlines prepared by publication in 
book form. 

In writing the book, three ideas have been kept constantly 
in mind: (1) to present the main scheme of analysis with¬ 
out the complication of special conditions; (2) to give 
working directions for each test rather than its description; 
and (3) to write the chemical equations for all reactions. 

No effort has been made to do more than the title implies, 
namely, to make this book a clear presentation of a good 
general scheme of analysis, without encumbering it with 
exhaustive special tests, or special analytical conditions. 
The author firmly believes that the beginner will find pro¬ 
gress very easy with this greatly simplified text. 

Exact directions, including the quantities of materials 
and reagents to be used, are given for each and every test. 
These have been specified with the object in view of forming, 
on the part of the student, the habit of using the minimum 
amount of material feasible and still insure good results. 

The unusually complete list of fundamental chemical 
equations make this book most helpful to the student. 
Even in cases where it is not used as the basic text it will 
iii 



IV 


Preface. 


be found most valuable as a reference book. All equations 
are written in the usual chemical form. This has been 
purposely done so that the student may have the practice 
of transforming them to the ionic form as he proceeds. 

This book is suitable for all students beginning Quali¬ 
tative Analysis in colleges and technical schools, while its 
simplicity and progression by easy steps will allow it to be 
used most successfully in second term high school work. 
There is a growing tendency to begin this subject in the 
high school course which the author hopes this book will 
encourage. 

Attention is especially called to the Introduction. Here 
the processes used in Qualitative Analysis, and the im¬ 
portant bearing of ionization upon this subject, are ex¬ 
plained. Introduction 4 gives the separation of the metals 
into groups. The consideration of this topic at this point 
not only gives the student a clear view of the general plan 
of analysis, before beginning the actual laboratory work, 
but it also places this separation in a convenient place for 
constant reference. 

The author invites friendly criticism of his work. He 
hopes that the subject matter here presented will prove as 
valuable to others as it has in his own classes, where it has 
been tested under varying conditions for some time and 
found most successful. 


Newark, N. J., 
March 15, 1921, 


F. C. R. 


TABLE OF CONTENTS. 


Introduction: 

1. The Ground Covered .. 1 

2. Ionization. 1 

3. Processes Used in Qualitative Analysis .... 3 

4. Separation of the Metals into Groups. 8 

5. The Written Record. 12 

Experiment: 

GROUP I. 

1. Tests for Lead. 15 

2. Tests for Mercurous Mercury. 18 

3. Tests for Silver. 20 

4. Separation of the HC1 Group. 22 

5. Analysis of an Unknown Solution. 24 

GROUP II, PART I. 

6. Tests for Mercuric Mercury. 26 

7. Tests for Lead. 28 

8. Tests for Bismuth. 31 

9. Tests for Copper. 35 

10. Tests for Cadmium. 38 

11. Separation of the H 2 S Group: Part I. 41 

12. Analysis of an Unknown Solution. 45 

13. Analysis of an Unknown Solution. 47 

GROUP II, PART II. 

14. Tests for Arsenic. 49 

15. Tests for Antimony. 52 


v 





















VI 


Contents. 


16. Tests for Tin. 56 

17. Separation of the H 2 S Group: Part II. . . . 60 

18. Analysis of an Unknown Solution. 63 

19. Analysis of an Unknown Solution. 65 

GROUP III. 

20. Tests for Chromium. 67 

21. Tests for Aluminum. 70 

22. Tests for Iron. 73 

23. Separation of the NH 4 OH Group. 77 

24. Analysis of an Unknown Solution. 80 

25. Analysis of an Unknown Solution. 81 

GROUP IV. 

26. Tests for Cobalt. 83 

27. Tests for Nickel. 86 

28. Tests for Manganese. 89 

29. Tests for Zinc. 92 

30. Separation of the (NH 4 ) 2 S 2 Group. 94 

31. Analysis of an Unknown Solution. 97 

32. Analysis of an Unknown Solution. 99 

GROUP V. 

33. Tests for Barium. 101 

34. Tests for Strontium. 104 

35. Tests for Calcium. 107 

36. Separation of the (NH 4 ) 2 C0 3 Group. 110 

37. Analysis of an Unknown Solution. 114 

38. Analysis of an Unknown Solution. 115 

GROUP VI. 

39. Tests for the Metals of the Sixth Group... 117 
























Contents. 


vii 

40. Analysis of an Unknown Solution: Sixth 

Group. 121 

41. Analysis of an Unknown Solution: All 

Groups. 122 

Introduction: 

6. The Acid Radicals. 123 

Experiment: 

42. Tests for Chlorates and Nitrates. 125 

43. Tests for Sulphides, Sulphites, Cyanides and 

Carbonates. 128 

44. Tests for Ferricyanides, Ferrocyanides, Sul¬ 

phates, Sulphites and Chlorides. 131 

45. Tests for Arsenites and Arsenates. 135 

Appendix: 

I. The Student’s Locker Equipment. 137 

II. Chemical Reagents needed for this Book. . 139 

III. Solids needed for the Preparation of Un¬ 
known Solutions. 142 












AN ELEMENTARY QUALITATIVE AN¬ 
ALYSIS OF THE METALS AND 
ACID RADICALS. 


INTRODUCTION. 


1. The Ground Covered. Qualitative analysis is the pro¬ 
cess of finding the ingredients of a mixture without regard 
to their amounts. In most analyses the metals are not 
present, as elements, but rather as salts of some of the 
commoner acids. 

Provision is made in this manual for the analysis of the 
following metals and acid radicals: 


Lead . 

Mercury (ous) . 
Silver . 

.Pb 
• Hg 
■ -Ag 

Arsenic .. 

Antimony . .. 
Tin . 

...Sb 
. ..Sn 

Cobalt . Co 

Nickel . Ni 

Manganese .... Mn 

7 Av \0 fin 

Mercury (ic) .., 

Bismuth . 

Copper . 

Cadmium . . . . 

..Hg 
. .Bi 
,.Cu 
. .Cd 

Chromium.... 
Aluminum..., 
Iron. 

..Cr 
, ..Al 
. ..Fe 


Barium . Ba 

Strontium . Sr 

Calcium . Ca 

■ Magnesium ... 

Sodium . 

Potassium .... 
Ammonium .., 

Sulphides . . . . 

...Mg 

...Na 

...K 

. ..nh 4 

. .S 

Chlorates . 

. .C10 3 

Ferrocyanides . FeC 6 N 6 

Nitrates .. 

..NO* 

Sulphites . 

...S0 3 

Ferricyanides . FeC 6 N 6 

Carbonates .... 

. .COs 

Chlorides. . . . 

. .Cl 

Arsenates . As0 4 

Cyanides . 

..CN 

Sulphates . . . . 

, ..so 4 

Arsenites.As0 3 


2. Ionization. Qualitative analysis is largely based upon 
the “Theory of Ionization.” This theory will now be 
briefly stated and explained. 


1 









































2 


Qualitative Analysis. 


Water, when pure, is not a conductor of the electric 
current. When, however, an acid, a base or a salt is dis¬ 
solved in it, even in small amounts, it at once becomes a 
conductor. Since these three classes of compounds have 
the power of rendering water a conductor they are called 
“ Electrolytes.” When electrolytes are put in water they 
at once ionize, that is, their molecules break into smaller 
groups of atoms called ions. It should be strongly empha¬ 
sized, at this point, that ionization is an action of the water 
alone upon the dissolving acid, base or salt. Students 
sometimes get the idea that it is necessary to pass an electric 
current through the solution before the ions will form. 
This is not so. All ions possess electric charges but these 
do not come from any outside source but rather from the 
molecule itself. Hydrogen and the metals, as ions, always 
have a plus electric charge while all other elements, and 
groups of elements, have a minus charge. 

When an acid ionizes, each atom of replaceable hydrogen 

4- 

forms an ion by itself. This H ion carries a single unit plus 
electric charge. The acid radical, the group left after 
removing the replaceable hydrogen, forms an ion by itself 
and carries as many units of minus electric charge as there 
are atoms of replaceable hydrogen in the acid. 

When bases ionize each hydroxyl (OH) radical contained 
in the base forms an ion and carries one unit minus charge. 
The metal atom of the base forms another ion and carries 
as many plus charges as there are hydroxyl radicals in the 
base. 

When a salt ionizes each atom of metal in the salt forms 
an ion by itself and carries as many plus charges as it has 
valence values in the salt from which it has just separated. 
The acid radical of the salt forms a single ion. It has as 


Introduction. 


3 


many minus charges as there are plus charges on all the 
metallic ions, from the salt molecule, combined. It is a 
significant fact that the number of unit electric charges, 
plus or minus, carried by an ion is always equal to the 
valence value of that ion. It should also be kept in mind 
that when a compound ionizes the sum of the plus charges 
on the hydrogen and metallic ions is always equal to the 
sum of the minus charges on all the other ions formed 
from the same molecule. 

As an illustration of what happens, as stated above, when 
ionization occurs the following examples are given. 
Sulphuric acid, H 2 S0 4 , when ionized gives: H . H . S0 4 . 
Calcium hydroxide, Ca(OH) 2 , when ionized gives: 

Ca . OH . OH. 

Lead nitrate, Pb(N0 3 )2, when ionized gives: 

Pb . NOs . N0 3 . 

Since the valence of an ion is always equal to the number 
of plus or minus charges it carries, it is quite usual to indi¬ 
cate the valence of elements and their important groups by 

+ 

writing these charges above their symbols, thus: Na, 

+++ + + 

Bi, Ca, etc. 

While it should be carefully noted that this theory of 
ionization is only a theory nevertheless no one today 
questions but that in the main at least it sets forth the 
facts as they are. Its essential facts should be fully mas¬ 
tered before proceeding with the actual work of qualitative 
analysis. 

3. Processes Used in Qualitative Analysis, (a) Solu¬ 
tion. This is a process for placing the substance under 


4 


Qualitative Analysis. 


test in the liquid state. When pure water is used for the 
solvent the process is usually mechanical only: no new 
substance is formed. When other reagents are used either 
alone or diluted with water it frequently happens that a 
chemical change occurs: some new substance has been 
formed which then dissolves in the solvent used. In either 
case the advantage is gained of having the substance in the 
liquid form. In this form, in general, substances react 
chemically more readily than they do in the solid state. 

If the substance under test is an ft Electrolyte ’’ it will 
ionize when placed in solution in water. This is a point of 
great importance as the spontaneous division of the mole¬ 
cules into ions readily allows these ions to form new com¬ 
binations. An illustration will make this point clear. 

When solid Pb(N0 3 )2 is dissolved in water three ions at 

+ + — — 

once are formed. These are Pb, (N0 3 ), and (N0 3 ). In 

+ 

like manner when HC1 is dissolved in water the ions H, 

and Cl are formed. If these two solutions are mixed these 
ions might recombine to form the original substances 
Pb(N0 3 ) 2 , and HC1 or they may quite as readily form the 
new compounds PbCl 2 , and 2HN0 3 . This actually occurs. 
The lead chloride, PbCl 2 , is not soluble in water or dilute 
nitric acid hence it separates out from the solution as an 

insoluble solid, called a precipitate. It is not long before 
^ + — 
this process removes all the Pb and Cl ions from the solu¬ 
tion, hence the new substance formed, PbCl 2 , is permanent. 
Reactions which behave in this way are said to run to 
completion. The chemical equation for this reaction is: 

Pb(N0 3 ) 2 + 2 HC1 -> | PbCl 2 + 2 HN0 3 . 

Ionization of test substances when placed in water is of 


Introduction. 


5 


great importance for another reason. When testing for 
lead, for example, it is immaterial what soluble compound 
of lead is present in the solution used, for as soon as this 
salt of lead dissolves in water it ionizes. Hence the test 
made is not for the compound in solution but for the 
lead ion. As these ions are all alike they respond to the 
same tests no matter what compound they come from. 
It should be made very emphatic that in qualitative analysis 
of the metals the 'ests used are largely tests for the ion of the 
metal. 

(6) Precipitation. When upon the addition of a chemi¬ 
cal reagent to the solution of some substance an insoluble 
solid separates, this solid is called a precipitate. This is a 
very important process in qualitative analysis. It is the 
basis of the analysis of most of the groups containing the 
metals. The color of this precipitate is frequently very 
characteristic. The solubility of the precipitate is fre¬ 
quently tested in various reagents. This usually throws 
much light upon its identity. Precipitates are also de¬ 
scribed and identified by the form they assume while in 
suspension in the liquid. These are described as: granular, 
like grains of sand; flocculent, woolly, remaining in suspen¬ 
sion in a loose, cloudlike mass; gelatinous, like jelly. 

(c) Filtration. This process is the separation of the 
suspended matter from a liquid and the matter contained 
in solution in this liquid. This process is usually carried 
out by passing the liquid through unglazed filter paper held 
in a glass funnel. For most work it is satisfactory to fold 
the paper along the line of one of its diameters and again at 
right angles to this line. By opening one of these folded 
pockets, a cone is formed which should accurately fit the 
glass funnel. When this is held in the funnel and thor¬ 
oughly wet the paper will adhere to the glass. Care should 
2 


u 


Qualitative Analysis. 


be exercised to exclude air-bubbles. If this is skillfully 
done a column of water will be held in the stem of the 
funnel; this increases the rapidity of the filtering process. 
The glass funnel, when in use, should be supported on a 
ring stand and the height adjusted so that the tip end of 
the stem touches the side of the beaker into which the liquid 
is passing. This liquid is called a filtrate. 

(d) Electro-deposition. When two metals are placed 
in an electrolyte and are brought in contact an electric 
current will flow from one to the other provided the electro¬ 
lyte acts chemically upon one of the metals. The metal 
from which the current flows within the liquid is said to be 
electropositive with respect to the metal toward which the 
current is flowing. The electromotive series including some 
of the commoner metals is as follows: 

1. Zinc 5. Iron 9. Copper 

2. Cadmium 6. Nickel 10. Silver 

3. Tin 7. Bismuth 11. Gold 

4. Lead 8. Antimony 12. Platinum 

Any metal preceding others in this list is electro-positive 
with respect to those which follow it. Thus zinc is electro¬ 
positive toward all other metals in the list. Bismuth is 
electro-positive toward antimony, copper, silver, gold and 
platinum, but electro-negative toward zinc, cadmium, tin, 
lead, iron and nickel. 

When two metals are thus connected in an electrolyte 
and a compound of a metal intermediate in the series is 
dissolved in this electrolyte then the electro-positive metal 
dissolves in the electrolyte and the metal in the electrolyte 
is deposited from its compound on the electro-negative 
metal. This principle is used in qualitative tests. An 
illustration will make this clear. Upon a small piece of 
platinum is placed a fe* drops of dilute HC1 in which is 


Intkoduction. 


7 


dissolved some compound of the metal antimony. A small 
piece of zinc is placed in this liquid and at the same time 
touches the platinum. In a few moments a characteristic 
stain of nearly black metallic antimony is deposited upon 
the platinum while the zinc slowly dissolves in the acid to 
replace the antimony which has been removed from the 
solution. This and other tests of the same kind are used 
to identify antimony and other metals. 

(e) Bead Tests. If a piece of platinum wire is sealed 
into the end of a short piece of glass tubing with about four 
inches of its length projecting beyond the glass and a small 
loop is made in the other end about one eighth of an inch 
in diameter and this loop is dipped in a little borax and 
then heated in the Bunsen flame a clear glass-like bead 
will be formed. If a trace of some cobalt compound is 
brought in contact with this bead and the bead is re-heated 
the cobalt will color it a beautiful blue color. This is a 
very delicate and characteristic test for cobalt. The 
chemical reactions which take place are as follows. When 
the borax is heated: 

Na 2 B 4 0 7 .10 H 2 O —> 2 NaB0 2 B 2 O 3 -J- 10 H 2 O. 

When cobalt chloride is heated in this bead: 

2 NaB0 2 d" B 2 O 3 -j- C 0 CI 2 *4" H 2 O 

+ A -> 2 NaB0 2 .Co(B0 2 ) 2 + 2 HC1. 

The water in this reaction is furnished by the flame or the 
atmosphere. The double sodium-cobalt metaborate, 2Na- 
B0 2 .Co(B0 2 )2, is the blue color. 

Beads are also made of other substances, viz., sodium 
carbonate and sodium-ammonium phosphate. Likewise a 


8 


Qualitative Analysis. 


number of metals besides cobalt impart color to these 
beads. Many of these are very characteristic of the metals 
involved and are much used to identify them. 

(/) Flame Tests. When a clean platinum wire 
mounted as in (e) is held in a Bunsen flame it imparts no 
mlor to the flame. If such a wire, however, is dipped into 
some compound of sodium and is then held in the Bunsen 
flame, the flame is colored yellow. Very minute quantities 
suffice to produce this effect. A number of the metals or 
their compounds will color the Bunsen flame. These color 
flame tests are all delicate and characteristic. They are 
much used to identify the metals which cause them, espe¬ 
cially sodium and potassium. Potassium colors the flame a 
peach blossom tint, a red-violet. Sodium if present covers 
up this color. If, /however, the Bunsen flame is viewed 
through a piece of blue glass the yellow rays of the sodium 
will be cut off and the presence or absence of the potassium 
may be observed. 

4. Separation of the Metals into Groups. When a solu¬ 
tion contains the compounds of a number of different metals, 
the first step in its analysis consists in dividing these metals 
into groups. Each group is then analyzed by itself. This 
greatly simplifies the work. In the groups that follow pro¬ 
vision is made for the analysis of twenty-two of the com¬ 
moner metals beside the ammonium radical, NH 4 , which 
in a considerable number of compounds acts the part of a 
metal. 

In order to understand this grouping let us suppose that a 
mixture containing soluble compounds of all these metals 
has been prepared. Practically all nitrates are soluble in 
water. We will suppose these have been used. The solu¬ 
tion will then contain ions of all these metals. If to a 
reasonable amount of this solution, say 10 cubic centi- 


Introduction. 


9 


meters, a few drops of dilute HC1 is added a white precipi¬ 
tate will at once form. This precipitate contains lead 
chloride, mercurous chloride and silver chloride. These 
compounds precipitate because they are insoluble in water 
and very dilute nitric acid and hydrochloric acid present 
in the solution at the same time. Since these are the only 
insoluble chlorides for the group of metals contained in this 
solution all other metallic ions remain in the solution. If 
sufficient HC1 is added the ions of mercury and silver will 
be completely removed from the solution. Some lead ions, 
however, will remain since lead chloride is sparingly soluble 
even in cold water. 

The first group is called “The Hydrochloric Acid Group.” 
It is removed from the solution by filtration. It contains: 

Lead Chloride.PbCl 2 

Mercurous Chloride . HgCl The Hydrochloric Acid Group. 
Silver Chloride.AgCl 

The filtrate from which the HC1 group has just been 
removed is now diluted with 60 c.c. of water, boiled, and a 
stream of sulphuretted hydrogen passed through it for some 
time. Eight of the ions still present in the mixture are 
capable of forming sulphides which are insoluble in dilute 
acid solutions. These are separated out by the H 2 S gas. 
Boil the mixture for a minute to coagulate the precipitate 
and then filter it hot. This second group has the following 
members; it is called the “Sulphuretted Hydrogen Group.” 


Mercuric Sulphide.HgS 

Lead “ PbS 

Bismuth “ Bi 2 S 3 The H 2 S Group: Part I. 

Copper “ CuS 

Cadmium “ CdS 









10 


Qualitative Analysis. 


Arsenic Sulphide.As 2 S 3 

Antimony “ .Sb 2 S 3 The H 2 S Group: Part 11. 

Stannous “ .SnS 


Boil the clear filtrate from this last filtration and again 
pass the H 2 S gas. No more precipitate should form. If it 
does add it to that already on the filter paper. Continue 
in this way until the group is entirely removed. Now boil 
the remaining clear solution down to 10 c.c. This step 
will concentrate the mixture and expel any H 2 S remaining 
in it. Concentrated nitric acid should now be added, a 
drop or two at a time, and the boiling continued as long as 
there is any change in the color of the mixture. This step 
oxidizes the ferrous compounds to ferric compounds and 
prepares the solution for the next step. Now add 10 c.c. 
of strong ammonium chloride solution and then dilute 
ammonium hydroxide until the mixture after boiling is 
decidedly alkaline. Continue the boiling for a minute to 
make the precipitation complete. Filter the mixture. The 
precipitate on the paper is called “The Ammonium Hy¬ 
droxide Group.” It contains: 


Chromium Hydroxide . . . .Cr(OH) 3 
Aluminum “ ... .Al(OH) 3 

Ferric “ ....Fe(OH) 3 


The Ammonium Hy¬ 
droxide Group. 


Boil the filtrate from which the ammonium hydroxide 
group has been completely removed down to 10 c.c. and 
add 20 c.c. of concentrated ammonium chloride solution 
to it. If the solution thus formed does not test alkaline 
with litmus add a few drops of dilute ammonium hydroxide. 
The mixture should be slightly alkaline. Now add 5 c.c. 
of yellow ammonium sulphide (dilute) and boil the resulting 





Introduction. 


11 


mixture slowly for two minutes and filter at once. This 
treatment precipitates out the sulphides of four more 
metals which are insoluble in dilute alkali. This fourth 
group is called “The Ammonium Sulphide Group.” This 
group contains: 


Cobalt Sulphide. CoS 

Nickel “ .NiS 

Manganese “ . MnS 

Zinc “ . ZnS 


The Ammonium Sulphide Group. 


To the filtrate obtained by removing the ammonium 
sulphide group add dilute HC1 in slight excess (litmus test) 
and boil for a minute to destroy any excess of ammonium 
sulphide which may remain. Filter again to remove any 
sulphur produced by the decomposition of the ammonium 
sulphide. Again make the solution decidedly alkaline 
with dilute ammonium hydroxide and then add ammonium 
carbonate solution as long as a precipitate forms. This 
treatment separates out three metals as carbonates. This 
fifth group is called “The Ammonium Carbonate Group.” 


Barium Carbonate.. . BaC0 3 
Strontium “ ...SrC0 2 

Calcium “ ... CaC0 3 


The Ammonium Carbon¬ 
ate Group. 


Filter out the ammonium carbonate group. The filtrate 
which remains is called “The Alkali Group.” It contains: 

Magnesium Compounds 
Sodium “ 

Potassium “ 

Ammonium “ 


.Mg 

.Na 

.K 

.NH 4 


(ions) 


The Alkali Group. 


12 


Qualitative Analysis. 


This last filtrate also contains all ammonium compounds 
added during the separation of the groups. For this 
reason tests for ammonium compounds are made in the 
original solution and not in the sixth group as we shall 
see later. 

Synopsis of Separation of the Metals into Groups. 

1 . 10 c.c. of Mixture + HC1 (dilute) in slight excess. Ppt. 

may be PbCl 2 , HgCl, AgCl. Group I. Filter. 

2 . Filtrate 1 + 60 c.c. of H 2 0 + boiling + H 2 S (excess), 

boil. Ppt. may be HgS, PbS, Bi 2 S 3 , CuS, CdS, As 2 S 3 , 
Sb 2 S 3 , SnS. Group II. Filter. 

3. Filtrate 2. Boil down to 10 c.c. + HN0 3 (cone.) few 

drops. Boil + 10 c.c. of NH 4 C1 + NH 4 OH (slight 
excess). Boil. Ppt. may be Cr(OH) 3 , Al(OH) 3 , 
Fe(OH) 3 . Group III. Filter. 

4. Filtrate 3. Boil down to 10 c.c. + 20 c.c. NH 4 C1 + 

NH 4 OH until slightly alkaline + 5 c.c. (NH 4 ) 2 S 2 . 
Boil. Ppt. may be CoS, NiS, MnS, ZnS. Group IV. 
Filter. 

5. Filtrate 4 add HC1 (dilute) in slight excess. Boil. 

Filter to remove sulphur + NH 4 OH to alkaline reac¬ 
tion + (NH 4 ) 2 C0 3 . Ppt. may be BaC0 3 , SrC0 3 , 
CaC0 3 . Group V. Filter. 

6 . Filtrate 5 may contain Mg, Na,K,NH 4 ions. Group VI. 
5. The Written Record. For convenience the laboratory 

work is divided into experiments. After each experiment 
is completed, before beginning the work of the next experiment , 
a written record of the work completed should be made. 
This should be in detail. When writing the record three 
lines of thought should be constantly kept in mind: what 
the experimenter did; what happened as a result of these 
steps taken; and the explanations of these happenings 


Introduction. 


13 


including chemical equations carefully written for all reac¬ 
tions. Check these to see that they balance in every case. 

The exact form of the written record is not material so 
long as it is clear and logical. The following form is sug¬ 
gested: Divide the laboratory record paper into three 
vertical columns. These should be headed: “ Operation ”— 
“Observation”—“ Conclusion.” If the result of each step 
taken is written in these columns in such a manner that the 
three parts of each are in a horizontal line across the paper 
the result will be found very satisfactory. Bear in mind 
that good laboratory records give the steps of the work in 
the same order in which they are taken. 

In the written records the following abbreviations may 
be freely used: 

Cubic centimeter.c.c. Concentrated.cone. 

Precipitate.ppt. V olume.vol. 

Test-tube.t.t. Gram.gm. 








14 


Qualitative Analysis. 


GROUP I. 

THE HYDROCHLORIC ACID GROUP. 

This group contains the metals whose chlorides are in¬ 
soluble in water and dilute acid. There are three of these: 


Lead.Pb 

Mercury (ous).Hg 

Silver.Ag 


When hydrochloric acid is added to solutions of soluble 
compounds of these metals they are precipitated out as 
chlorides: PbCl 2 , HgCl and AgCl. 

In the study of the group tests for the individual metals 
will first be given under Experiments 1-3 and then a 
method for identifying these metals will be given when they 
are mixed in a solution in Experiment 4. An unknown 
solution will be analyzed in Experiment 5. 

Note: Unless more definitely specified, volumes of solu¬ 
tions to be used given in cubic centimeters will be measured 
approximately in a standard 6" x f " test-tube. These 
tubes hold about 30 c.c. Each inch of length of the tube 
will have a volume of approximately 5 c.c. 





Group 1. 


lo 


Experiment 1. 

Title: Tests for lead. Symbol Pb. Valence 2. 

Note: Success in “Qualitative Analysis” is absolutely 
dependent upon scrupulous cleanliness, and great exactness 
in following out every detail of the directions given, to the 
letter. The student will save many hours of labor and 
much disappointment if these two points are emphasized 
and carefully followed from the start. 

Form the habit of washing a piece of apparatus as soon 
as it is empty. Nearly all chemicals used are easily removed 
before they dry on the surface of the test-tube, beaker, or 
dish, with running water. Many are difficult to remove 
after standing. 

A. 1 . Lead Chloride. Pour 5 c.c. of lead nitrate, Pb- 
(N0 3 ) 2 , solution into a test-tube (one inch in the tube). 
Add dilute hydrochloric acid, HC1, a few drops at a time 
so long as a precipitate continues to form. This precipitate 
is lead chloride (white), PbCl 2 , which forms because lead 
chloride does not dissolve freely in cold water or very dilute 
acids. 

This reaction written in chemical form is: 

Pb(N0 3 ) 2 + 2 HC1 -> PbCl 2 1 + 2 HN0 3 . 

In the ionic form this reaction is written: 

Pb. (NO.). (NO,) + H.C1.H.C1 -» PbCl 2 1 

+ H.(N0 3 ).H.(N0 3 ). 

2. Potassium Chromate Precipitates Lead Chromate. 

Filter the contents of the test-tube just prepared in (1). 
Discard the filtrate if it is clear. Pour it through the filter 


16 


Qualitative Analysis. 


again if it is not and continue doing this until it is clear, 
then discard it. Pour 15 c.c. of boiling water through the 
filter paper. This will wash the excess HC1 from the filter 
paper and also dissolve most of the lead chloride precipitate. 
(PbCU dissolves readily in hot water.) Catch this hot 
water as it runs through the filter paper in a test-tube and, 
wheii filtration is complete, add a few drops of potassium 
chromate solution, K 2 Cr0 4 , to it. If a yellow precipitate 
forms it is lead chromate, PbCr0 4 , a delicate and very 
characteristic test for lead. The reactions in the chemical 
and in the ionic form are as follows: 

PbCl 2 + K 2 Cr0 4 -> PbCr0 4 1 -» 2 KC1. 

Pb.ci.ci + K.K.Cr0 4 ->PbCr0 4 [ + K.C1.K.CL 

3. Insoluble Basic Lead Chloride. If any precipitate re¬ 
mains on the filter paper, pour 5 c.c. of dilute ammonium 
hydroxide, NH 4 OH, through it. This treatment will not 
dissolve lead chloride but will change it into a very insoluble 
basic lead chloride, PbCl(OH). The reaction is as follows: 

PbCl 2 + NH 4 OH -> PbCl(OH) 1 + NH 4 C1. 

Pb.ci.ci + NH 4 .OH -> PbCl(OH) I + NH 4 .C1. 

If the hot water used in (2) dissolved all the lead chloride 
then more should be prepared as in (1) and the test with 
the ammonium hydroxide made with this after washing it 
with cold water. Lead chloride is only slightly soluble in 
cold water. 

Conclusions, (a) HC1 precipitates PbCl 2 (white). 

( b ) PbCl 2 is somewhat soluble in cold water and dissolves 
readily in hot water. 


Group I. 


17 


(c) K 2 Cr0 4 precipitates PbCr0 4 (yellow). 

(d) NH 4 OH changes PbCl 2 to insoluble PbCl(OH) 
(cream white). 

These four tests serve to completely identify lead ion. 
No other substance known will give the same combination 
of tests. Of the other members of this group, mercurous 
mercury gives test (a) but none of the others. Silver will 
respond to tests (a) and (c) but not to the others. 

Note: In all written records the student should change 
the equations written in the manual in the chemical form 
and write them in the ionic form. See Introduction 2. 


18 


Qualitative Analysis. 


Experiment 2. 

Title: Tests for mercurous mercury. Symbol Hg. 
Valence 1 . 

A. 1 . Mercurous Chloride. Pour 5 c.c. of a solution of 
mercurous nitrate, HgN0 3 , into a test-tube. Add dilute 
hydrochloric acid, HC1, a few drops at a time as long as a 
precipitate forms. This white precipitate is mercurous 
chloride, calomel, HgCl. The reaction is as follows: 

HgN0 3 + HC1 HgCl | + HN0 3 . 

2. Action of Ammonium Hydroxide on Mercurous 
Chloride. Filter the contents of the test-tube. Discard 
the filtrate when it is clear. Wash the precipitate by pour¬ 
ing 15 c.c. of hot or cold water through the filter paper. 
Mercurous chloride is insoluble in both. Compare with 
lead chloride. Now pour 5 c.c. of dilute ammonium 
hydroxide through the filter in such a manner as to wet all 
the precipitate on the paper with it. The precipitate at 
once turns a gray-black color due to the formation of 
metallic mercury very finely divided throughout a new 
white substance formed at the same time known as amino- 
mercuric chloride, HgClNH 2 . The reaction is as follows: 

2 HgCl + 2 NH 4 OH -> Hg + HgClNH 2 

+ NH 4 CI + 2 H 2 0. 

This is a very characteristic test and serves well to identify 
the mercurous ion. 

Conclusions, (a) HC1 precipitates HgCl (white). 

(b) HgCl is insoluble in hot and cold water. 


Group 1. 


19 


(c) NH 4 OH turns HgCl gray-black and insoluble, in 
dilute NH4OH. 

These three tests serve to identify mercurous mercury. 
No other substance responds to all three tests. 

Lead shows test (a) only. 

Silver responds to tests (a) and (b). 


20 


Qualitative Analysis. 


Experiment 3. 

Title: Tests for silver. Symbol Ag. Valence 1. 

A. 1. Silver Chloride. Pour 5 c.c. of silver nitrate solu¬ 
tion, AgN0 3 , into a test-tube. Add dilute hydrochloric 
acid, HC1, a few drops at a time as long as a precipitate 
forms. This precipitate is silver chloride, AgCl (white). 
The reaction is as follows: 

AgN0 3 + HC1 -> AgCl 1 + HN0 3 . 

2. Filtering Silver Chloride. Filter the contents of the 
test-tube. Some difficulty may be experienced with the 
AgCl, which is very finely divided, passing through the 
filter paper. Pouring the mixture through the filter a 
number of times will usually prove successful. The addi¬ 
tion of a number of crystals of ammonium nitrate and the 
application of gentle heat to the mixture before filtration is 
usually effective. Discard the clear filtrate. Wash the 
precipitate with 15 c.c. of hot or cold water. Silver chloride 
is insoluble in both hot and cold water. 

3. Action of Ammonium Hydroxide on Silver Chloride. 
Pour 5 c.c. of dilute ammonium hydroxide, NH 4 OH, through 
the filter paper. It should come in contact with all the 
AgCl. This will at once dissolve the silver chloride due to 
the formation of very soluble ammonio-silver chloride, 
Ag(NH 3 ) 2 Cl. 

The reaction is as follows: 

AgCl + 2 NH 4 OH -> Ag(NH 3 ) 2 Cl + 2 H 2 0. 

To this filtrate add dilute nitric acid, HN0 3 , in excess (to 
acid reaction: test with litmus paper). A white precipitate 


Group I. 


21 


of silver chloride, AgCl, will form. The reaction is as 
follows: 

Ag(NH 3 ) 2 Cl + 2 HN0 3 -» AgCl | + 2 NH 4 N0 3 . 

This is a very characteristic test and will identify the silver 
ion. 

Conclusions, (a) HC1 precipitates AgCl (white). 

(6) AgCl is insoluble in both hot and cold water. 

(c) AgCl dissolves in NH 4 OH forming very soluble 
Ag(NH 3 ) 2 Cl. 

(d) HN0 3j in excess, reprecipitates the insoluble AgCl. 
These four tests completely identify the silver ion. No 

other substance known will give the same combination of 
tests. 

Lead gives test (a) only. 

Mercurous mercury responds to tests (a) and (6) but not 
(c) and ( d ). 


22 


Qualitative Analysis. 


Experiment 4. 

Title : Separation of the metals of the hydrochloric acid 
group. The solution used is known to contain Pb, Hg, 
and Ag ions. 

1. Precipitation of the Group. Pour 5 c.c. of the solution 
containing the group into a test-tube and add dilute hydro¬ 
chloric acid, a few drops at a time, as long as a precipitate 
continues to form. Filter. Discard this clear filtrate. If 
the filtrate is not clear continue passing it through the same 
filter until it is. The precipitate on the filter paper con¬ 
tains PbCl 2 , HgCl and AgCl. 

2. Tests for Lead. Wash the precipitate by passing 15 
c.c. of hot water through the filter. To this hot water 
filtrate add a few drops of potassium chromate solution. 
The formation of a yellow precipitate of lead chromate 
indicates the presence of lead. 

Pour a second 15 c.c. of hot water through the filter paper. 
To this hot water filtrate add a few drops of dilute sulphuric 
acid and then bring the mixture to a boil. If a white 
precipitate forms it is insoluble lead sulphate. It confirms 
the presence of lead. 

3. Tests for Mercurous Mercury. Pour 5 c.c. of dilute 
ammonium hydroxide through the precipitate remaining 
on the filter paper. If the liquid which passes through the 
filter is not clear continue passing it through the filter until 
it is. Reserve this clear filtrate for (4). The precipitate 
on the filter paper will now be a gray-black color due to 
the formation of some metallic mercury. (See Experi¬ 
ment 2.) This black color indicates the presence of mercury 
(mercurous ion). 

4. Tests for Silver. Add dilute nitric acid, to acid reac¬ 
tion, to the filtrate reserved from (3). A white precipitate 


Group I. 


23 


which forms is silver chloride and indicates the presence of 
silver . Use litmus paper as an indicator. 

Conclusions, (a) For the explanation of each test used 
in this separation the student is referred to experiments 1-3. 

(b) The written record of this experiment should include 
explanations of every step as well as the steps themselves. 

(c) All reactions occurring in this separation should be 
written out in equation form as a part of the written record. 
Nearly all of these equations will be found in experiments 
1-3. 


24 


Qualitative Analysis. 


Experiment 5. 

Title: Separation of the metals of the hydrochloric acid 
group. The content of this solution is unknown. 

1. Directions. Follow the directions for the analysis of 
this group given for the known solution in experiment 4. 
Keep a carefully written record of the metals you find 
present. Do not trust your memory even for the simplest 
analysis. It is unnecessary to write out the scheme of 
analysis for each unknown solution analyzed after this has 
been done once for the known solution. 

2. The Written Record. A brief and very satisfactory 
method for recording an analysis of the hydrochloric acid 
group is as follows: 


The Group. 

Pb. 

Hg. 

Ag. 

Add HC1 in ex¬ 

Filtrate 1. 

Residue 1. 

Filtrate 3. 

cess. 

Add K 2 CrC>4. 

Pour NH 4 OH 

Add HNOa in 

Filter. 

Yellow ppt. is 

through it. 

excess. 

Wash ppt. with 

PbCr0 4 . 

Black residue is 

White ppt. is 

hot H 2 0. 

Indicates lead. 

Hg. 

AgCl. 

Reserve filtrate 1. 

Wash again. 
Reserve filtrate 2. 
Reserve residue 
on filter paper 
in funnel. 

Filtrate 2. 

Add H 2 S0 4 . 
White ppt. is 
PbS0 4 . 

Confirms lead. 

Indicates mer¬ 
cury (ous). 
Reserve filtrate 
3. 

Indicates silver. 


Note: When a metal is not present in a mixture it will 
be found satisfactory to write this fact in the proper column 
which is otherwise left blank. For example: If lead is 
missing the column headed Pb should contain only the 
statement “No lead found.” 









Group II— Part I. 


25 


GROUP II. 

THE SULPHURETTED HYDROGEN GROUP: PART I. 

This group contains the metals whose sulphides are insol¬ 
uble in water and dilute acids (cold), and also insoluble in 
warm, dilute, yellow ammonium sulphide. There are five 


of these: 

Mercury (ic).Hg 

Lead.Pb 

Bismuth.Bi 

Copper.Cu 

Cadmium.:.. Cd 


When sulphuretted hydrogen gas is allowed to bubble 
slowly through a hot dilute mixture of any soluble com¬ 
pounds of these metals, which has been made slightly acid 
with nitric or hydrochloric acids, these metals are precipi¬ 
tated out of the solution as sulphides: HgS, PbS, Bi 2 S 3 , 
CuS and CdS: 

Note: Introduction 3: “Ionization” should be read 
again at this point. 







26 


Qualitative Analysis. 


Experiment 6. 

Title: Tests for mercuric mercury. Symbol Hg. Val¬ 
ence 2. 

A. 1 . Mercuric Sulphide. Pour 5 c.c. of a solution of 
mercuric nitrate into a test-tube. Add a few drops of 
dilute nitric acid. Warm this mixture and pass sulphur¬ 
etted hydrogen gas into it for 10 seconds. Empty the con¬ 
tents of this test-tube into a beaker. Fill the same test- 
tube with water and add this to the contents of the beaker. 
This will dilute the solution. Bring the contents of the 
beaker to a boil and again pass sulphuretted hydrogen gas 
through the mixture until precipitation appears to be com¬ 
plete. If a Kipp or other form of automatic generator is 
used for the gas, use only a slow stream of gas, as the gas 
which bubbles out into the air is, of course, wasted. Such a 
generator is not essential but will be found very convenient. 
Filter. Discard the filtrate. Wash the precipitate three 
times with hot water. Use a wash bottle for this purpose. 
Reserve the precipitate. It is mercuric sulphide, HgS. 
The reaction is as follows: 

Hg(N0 3 ) 2 + H 2 S -> HgS 1 + 2 HN0 3 . 

2. Mercuric Sulphide is Insoluble in Hot Dilute Nitric 
Acid. Remove the filter paper from the funnel and place 
that portion of it containing the precipitate in an evapor¬ 
ating dish and add 10 c.c. of dilute nitric acid (1-3). Bring 
this mixture to a boil but do not allow it to continue boiling. 
Mercuric sulphide is not soluble in hot dilute nitric acid. 
The sulphides of the other metals in this group dissolve 
readily in this solvent. This fact is made use of in the 
analysis of the group for the separation of mercuric mercury 
from the metals Pb, Bi, Cu and Cd. 


Group II— Part I. 


27 


B. 1. The Stannous Chloride Test. Pour 5 c.c. of a solu¬ 
tion of mercuric nitrate into a test-tube and add a few 
drops of dilute hydrochloric acid to it and then a drop or 
two of stannous chloride solution, SnCl 2 , when a white 
precipitate of mercurous chloride will form. Thus: 

Hg(N0 3 ) 2 + SnCl 2 -> HgCl 2 + Sn(N0 3 ) 2 , 

and 

2 HgCl 2 + SnCl 2 -> 2 HgCl I + SnCl 4 . 

Continue adding the stannous chloride solution until 5 c.c. 
have been used. Upon standing or slight heating the white 
precipitate of HgCl formed as shown above will rapidly 
darken until the mixture in the test-tube is a dark gray 
color. This color is due to the presence of finely divided 
metallic mercury formed by the further reduction of the 
mercurous chloride. The reaction is: 

2 HgCl + SnCl 2 -> 2 Hg 1 + SnCl 4 . 

Reserve the contents of this test-tube for (2). 

This test is exceedingly characteristic of mercury and 
may be used to identify it even in the presence of the other 
members of this group. 

2. Boiling the mixture reserved above will sometimes 
result in the formation of a globule of metallic mercury. 
This makes the test still more conclusive. Try it. 

Conclusions. 1. H 2 S precipitates HgS (black) from an 
acid solution. HgS is insoluble in hot dilute nitric acid. 

2 . SnCl 2 reduces soluble HgCl 2 to insoluble HgCl (white). 
SnCl 2 reduces HgCl to Hg (gray). 


28 


Qualitative Analysis. 


Experiment 7. 

Title: Tests for lead (continued). Note: See experi¬ 
ment 1. 

A. 1. Lead Sulphide. Pour 5 c.c. of lead nitrate solu¬ 
tion into a test-tube. Add a few drops of dilute nitric 
acid and warm the mixture. Pass sulphuretted hydrogen 
gas through the contents of the tube for 10 seconds. Pour 
the contents of the test-tube into a beaker and dilute them 
with a test-tube full of water. Bring the contents of the 
beaker to a boil and pass sulphuretted hydrogen gas through 
them until precipitation is judged to be complete. The 
precipitate formed is lead sulphide. The reaction is as 
follows: 

Pb(N0 3 ) 2 + H 2 S -> PbS | + 2 HN0 3 . 

Boil the contents of the beaker again for a few seconds 
and filter at once. Discard the clear filtrate. This second 
boiling just before filtering expels the excess H 2 S and 
coagulates the precipitate which causes the filtration to be 
much more complete and rapid. Reserve the precipitate. 

2. Lead Sulphide is Soluble in Hot Dilute Nitric Acid. 
Wash the precipitate of lead sulphide three times with hot 
water. Use a wash bottle. If the H 2 S is not thoroughly 
washed away before the next step is taken sulphur will be 
precipitated when the acid is added. Thus: 

2 HN0 3 + 3 H 2 S 4 H 2 0 + 2 NO + 3 S. 

Place that portion of the filter paper containing the 
precipitate in an evaporating dish and add 10 c.c. of dilute 
nitric acid (1 to 3). Bring the contents of the dish to a 
boil. The lead sulphide will be completely dissolved. 
Thus: 


PbS + 2 HN0 3 -> Pb(N0 3 ) 2 + H 2 S. 


Group II— Part I. 


29 


Note the formation of a small amount of H 2 S in the reac¬ 
tion just given. This will invariably react with the HN0 3 . 
used to dissolve the PbS, as shown above, with the forma¬ 
tion of a small amount of sulphur. This sulphur usually 
contains enough PbS through it to color it black. This 
might lead the pupil to think that the precipitate of lead 
sulphide was not completely soluble in the nitric acid. 
No confusion need arise at this point as the sulphur formed 
as stated floats upon the nitric acid while the heavy lead 
sulphide quickly settles to the bottom of the dish. 

B. 1 . Sulphuric Acid Precipitates Lead Sulphate. Pour 
5 c.c. of lead nitrate solution into a test-tube. Add dilute 
sulphuric acid until precipitation is judged to be complete. 
The precipitate formed is lead sulphate, white. The reac¬ 
tion is: 

Pb(N0 3 ) 2 + H 2 S0 4 -> PbS0 4 1 + 2 HN0 3 . 

Filter and discard the clear filtrate. Reserve the precipi¬ 
tate. 

2. Distinction Between Lead Sulphate and Bismuth 
Oxy-sulphate. Since sulphuric acid may precipitate the 
white bismuth oxysulphate, (Bi0) 2 S0 4 , when this test is 
used in a mixture containing the group, this test should 
always be confirmed. To do this wash the precipitate free 
from sulphuric acid. Pour 5 c.c. of warm ammonium ace¬ 
tate solution through the filter paper. Continue doing this 
until the white precipitate is dissolved. To this solution 
add a few drops of potassium chromate solution. If a 
yellow precipitate forms it is probably lead chromate but 
it might be bismuth chromate. To determine this point 
add an equal volume of acetic acid to the contents of the 
test-tube and shake. Lead chromate is not soluble in 
acetic acid while bismuth chromate, if present, would 


30 


Qualitative Analysis. 


dissolve at once. The equation for the solution of lead 
sulphate in ammonium acetate solution is as follows: 

PbS0 4 + 2 CH 3 COONH 4 -> (CH 3 COO) 2 Pb + (NH 4 ) 2 S0 4 . 

The equation for the precipitation of lead chromate is: 

(CH 3 COO) 2 Pb + K 2 Cr0 4 -> PbCr0 4 1 + 2 CH 3 COOK. 

When the presence of lead only is to be determined the 
lead sulphate may be dissolved in a mixture of equal parts 
of ammonium acetate and acetic acid and a few drops of 
potassium chromate added. In this case no precipitate 
will be formed unless lead is present. 

Conclusions. 1 . H 2 S precipitates PbS (black). 

2. PbS is soluble in hot dilute nitric acid. Pb(N0 3 ) 2 is 
formed. 

3. H 2 S0 4 precipitates PbS0 4 (white). 

4. PbS0 4 dissolves in CH 3 COONH 4 and is reprecipitated 
by the addition of a few drops of K 2 Cr0 4 . PbCr0 4 (yellow) 
is formed. PbCr0 4 is insoluble in CH 3 COOH. 


Group II— Part I. 


31 


Experiment 8. 

Title: Tests for bismuth. Symbol Bi. Valence 3. 

A. 1. Bismuth Sulphide. Pour 5 c.c. of a solution of bis¬ 
muth nitrate into a test-tube. Add a few drops of dilute 
nitric acid. Warm this mixture and pass sulphuretted 
hydrogen gas through it for 10 seconds. Now empty the 
contents of the test-tube into a beaker. Fill the same 
test-tube with water and add this to the beaker, to dilute 
the solution. Boil this solution and then pass sulphuretted 
hydrogen gas through it until precipitation appears to be 
complete. Again boil the contents of the beaker to expel 
the excess H 2 S and then filter. Discard the clear filtrate. 
Wash the precipitate on the filter paper three times with 
hot water. Reserve this precipitate of bismuth sulphide. 
The reaction for its formation is as follows: 

2 Bi(N0 3 ) 3 + 3 H 2 S -> Bi 2 S 3 1 + 6 HN0 3 . 

2. Bismuth Sulphide is Soluble in Hot Dilute Nitric Acid. 

Remove the filter paper, reserved above, from the funnel 
and place the part containing the precipitate in an evapor¬ 
ating dish and add 10 c.c. of dilute nitric acid. Bring this 
mixture to a boil. The bismuth sulphide will dissolve. 
The reaction is: 

Bi 2 S 3 + 6 HNOa -» 2 Bi(N0 3 ) 3 + 3 H 2 S. 

B. Reaction of Bismuth Chloride with Water. Add two 

or three drops of a strong solution of bismuth chloride to a 
test-tube full of cold water. A white flocculent precipitate 
of bismuth oxy-chloride will form. The reaction is: 

BiCl 3 + H 2 0 -> BiOCl | + 2 HC1. 


32 


Qualitative Analysis. 


This reaction is very characteristic of bismuth. Only a 
few other metals give this reaction at all, and none so 
readily as bismuth. 

C. 1. Bismuth Oxy-Hydroxide. Pour 5 c.c. of bismuth 
nitrate solution into a test-tube and add dilute ammonium 
hydroxide a few drops at a time as long as a white pre¬ 
cipitate continues to form. The reaction is: 

Bi(N0 3 ) 3 + H 2 0 -> BiO(NOa) + 2 HN0 3 , 

and 

BiO(NOs) + NH 4 OH -> BiO(OH) | + NH 4 N0 3 . 

Add an excess of ammonium hydroxide to the mixture in 
the test-tube and shake the contents of the tube. Bismuth 
oxy-hydroxide is not soluble in an excess of ammonium 
hydroxide. This is an important point. Ammonium 
hydroxide precipitates both copper and cadmium hydroxides 
and both of these precipitates dissolve readily in an excess 
of the ammonium hydroxide. 

2 . Preparation of Sodium Stannite. Filter the contents 
of the test-tube just used in (1). Wash the precipitate 
on the filter paper thoroughly. Reserve this precipitate 
for (3). 

Prepare some sodium stannite (Na 2 Sn0 2 ) solution as 
follows: to 3 c.c. of stannous chloride solution in a test- 
tube add sodium hydroxide solution a drop or two at a time 
until a precipitate, which remains upon shaking, forms. 
This precipitate is stannous hydroxde. The reaction is: 

SnCl 2 + 2 NaOH -> Sn(OH) 2 J + 2 NaCl. 

Continue adding the sodium hydroxide a few drops at a 
time until the stannous hydroxide precipitate dissolves in 


Group II— Part I. 


33 


the excess of the base with the formation of sodium stannite 
solution. The reaction is: 

Sn(OH) 2 + 2 NaOH -> Na 2 Sn0 2 + 2 H 2 0. 

Sodium stannite is an unstable compound and must be 
prepared in the manner just described immediately before 
use. Reserve this solution for (3). 

3. The Sodium Stannite Test. Place the test-tube con¬ 
taining the sodium stannite solution under the funnel con¬ 
taining the bismuth oxy-hydroxide precipitate, which has 
been carefully washed , and pour 10 or 12 drops of dilute 
hydrochloric acid through the precipitate allowing this 
liquid to drop into the sodium stannite solution. Black 
particles of metallic bismuth form where the hydrochloric 
acid meets the sodium stannite solution. This is a delicate 
and exceedingly characteristic test for bismuth. The reac¬ 
tions which take place are as follows: 

First the bismuth oxy-hydroxide dissolves in the hydro¬ 
chloric acid with the formation of bismuth chloride, 

BiO(OH) + 3 HC1 -> BiCl 3 + 2 H 2 0. 

Then the bismuth chloride reacts with the sodium stannite 
and some sodium hydroxide forming metallic bismuth, 
sodium stannate, sodium chloride and water. Thus: 

2 Bids + 3 Na 2 Sn0 2 + 6 NaOH -> 2 Bi 

+ 3 Na 2 Sn0 3 + 6 NaCl + 3 H 2 0. 

The white precipitate formed at the same time the black 
particles of metallic bismuth appear is stannous hydroxide. 
This is caused by action of the excess hydrochloric acid 


34 Qualitative Analysis. 

used to dissolve the bismuth oxy-hydroxide. The reaction 
is: 

Na 2 Sn0 2 + 2 HC1 -> 2 NaCl + Sn(OH) 2 \. 

The sodium hydroxide called for by the equation above 
may be excess base used in preparing the sodium stannite, 
or it may be produced by the hydrolysis of the sodium 
stannite itself. Thus: 

Na 2 Sn0 2 + 2 H 2 0 -> 2 NaOH + Sn(OH) 2 1. 

Conclusions. 1. H 2 S precipitates Bi 2 S 3 from acid solu¬ 
tions. 

2. Bi 2 S 3 is soluble in hot dilute HN0 3 . 

3. H 2 0 reacts with BiCl 3 to form BiOCl (white). 

4. NH 4 OH precipitates BiO(OH) (white). Insoluble in 
excess. 

5. Na 2 Sn0 2 reduces BiCl 3 to metallic Bi (black particles). 


Group II— Part I. 


35 


Experiment 9. 

Title: Tests for copper. Symbol Cu. Valence 2. 

A. 1 . Copper Sulphide. Pour 5 c.c. of a solution of 
copper nitrate into a test-tube. Add a few drops of dilute 
nitric acid. Warm the mixture and pass sulphuretted 
hydrogen gas through it for 10 seconds. Pour the contents 
of the test-tube into a beaker and dilute them with a test- 
tube full of water. Bring this mixture to a boil and pass 
sulphuretted hydrogen through it for a minute or until pre¬ 
cipitation is judged to be complete. Again boil the con¬ 
tents of the beaker to expel excess sulphuretted hydrogen 
and filter. Discard the clear filtrate. Reserve the pre¬ 
cipitate of copper sulphide on the filter paper. It should 
be washed three times with hot water. Use a wash bottle. 
The reaction for the precipitation of the copper sulphide is: 

Cu(N0 3 ) 2 + H 2 S -» CuS 1 + 2 HN0 3 . 

2. Copper Sulphide is Soluble in Hot Dilute Nitric Acid. 

Put as much of the filter paper reserved from (1) as is 
covered with precipitate in an evaporating dish and add 
10 c.c. of dilute nitric acid. Bring this mixture to a boil. 
The copper sulphide readily dissolves in the acid. The 
reaction is: 


CuS + 2 HN0 3 -> Cu(N0 3 ) 2 + H 2 S. 

B. 1. Pour 5 c.c. of copper nitrate solution into a test- 
tube and add dilute ammonium hydroxide one drop at a 
time. Note the light blue precipitate of copper hydroxide 
which forms. The reaction is: 

Cu(N0 3 ) 2 + 2 NH 4 OH -» Cu(OH) 2 i + 2 NH 4 N0 3 . 


36 


Qualitative Analysis. 


Now add an excess of ammonium hydroxide to this pre¬ 
cipitate in the test-tube and shake the mixture. The 
copper hydroxide precipitate at once dissolves in the excess 
of the ammonium hydroxide with the formation of a fine 

dark blue solution of ammonio-cupric hydroxide. The 

+ + 

complex ion Cu(NH 3 ) 4 causes the blue color. 

Cu(OH) 2 + 4 NH 4 OH -> Cu(NH 3 ) 4 (OH) 2 + 4 H 2 0. 

This test is very characteristic of copper. A more delicate 
confirmatory test for copper may be made as directed in (2). 
Reserve this blue solution for (2). 

2. A Confirmatory Test for Copper. Acidify 5 c.c. of the 
blue solution reserved from (1) with acetic acid. The 
reaction is: 

Cu(NH 3 ) 4 (OH) 2 + 6 CH3COOH -> (CH 3 COO) 2 Cu 

+ 4 CH 3 COONH 4 + 2 H 2 0. 

Add one drop of potassium ferrocyanide solution. The 
formation of a red precipitate of cupric ferrocyanide indi¬ 
cates copper. The reaction is: 

2 (CH 3 COO) 2 Cu + K 4 Fe(CN) 6 -> Cu 2 Fe(CN) 6 l 

+ 4 CH 3 COOK. 

If the amount of copper present is very small add an 
excess of the potassium ferrocyanide and filter the solution. 
Wash the precipitate carefully on the filter paper. A pink 
color on the filter paper indicates copper. 

It should be borne in mind that potassium ferrocyanide 
also precipitates cadmium if that metal is present. The 
copper salt is less soluble, however, and hence precipitates 


Group II— Part I. 


37 


out first. Hence the reason for adding one drop of the 
reagent at first. Also the precipitate of cadmium ferro- 
cyanide is white hence when the mixed precipitates are 
examined upon a white filter paper the cadmium salt is 
not seen. This test will show amounts of copper so small 
that the ammonium hydroxide blue color test fails. 

C. An Electrolytic Test for Copper. Acidulate 5 c.c. of a 
solution of copper nitrate or other copper salt with a few 
drops of dilute hydrochloric acid. Add two or three small 
iron nails to this solution and gently warm it. In a few 
moments the iron nails will be covered with a coating of 
metallic copper. This copper color is very characteristic. 
The reaction is: 

CuCl 2 + Fe -> FeCl 2 + Cu. 

Conclusions. 1. H 2 S precipitates CuS from acid solu¬ 
tions. 

2 . CuS is soluble in hot dilute HN0 3 . 

3. NH 4 OH precipitates Cu(OH ) 2 (light blue). 

4. Cu(OH ) 2 is soluble in an excess of NH 4 OH, forming 
Cu(NH 3 ) 4 (OH) 2 . 

5 . K 4 Fe(CN ) 6 precipitates Cu 2 Fe(CN ) 6 (red) from acid 
solutions. 

6 . Fe replaces Cu from acid solutions depositing Cu on 
the Fe. 


4 


38 


Qualitative Analysis. 


Experiment 10. 

Title: Tests for Cadmium. Symbol Cd. Valence 2. 

A. 1 . Cadmium Sulphide. Pour 5 c.c. of a solution of 
cadmium nitrate into a test-tube. Add a few drops of 
dilute nitric acid. Warm this mixture and pass sulphur¬ 
etted hydrogen gas through it for 10 seconds. Pour the 
contents of the test-tube into a beaker and dilute with a 
test-tube full of water. Now bring the contents of the 
beaker to a boil. Again pass sulphuretted hydrogen gas 
thiough the diluted solution until precipitation is judged 
to be complete. The yellow precipitate formed is cadmium 
sulphide. The reaction is: 

Cd(N0 3 ) 2 + H 2 S -> CdS 1 + 2 HN0 3 . 

Filter. Discard the clear filtrate. Wash the precipitate 
three times with hot water and reserve it for (2). 

2. Cadmium Sulphide is Soluble in Hot Dilute Nitric 
Acid. Place the filter paper containing the precipitate 
reserved from (1) in an evaporating dish and add 10 c.c. of 
dilute nitric acid. Bring this mixture to a boil. The 
cadmium sulphide dissolves readily. The reaction is: 

CdS + 2 HN0 3 -> Cd(N0 3 ) 2 + H 2 S. 

B. 1 . Cadmium Hydroxide. Pour 5 c.c. of cadmium 
nitrate solution into a test-tube and add one drop of dilute 
ammonium hydroxide. Shake. Continue adding the am¬ 
monium hydroxide one drop at a time until a white pre¬ 
cipitate of cadmium hydroxide forms. The reaction is: 

Cd(N0 3 ) 2 + 2 NH 4 OH -> Cd(OIi) 2 1 + 2 NH 4 N0 3 . 


Group II—Part I. 


39 


2. Add an excess of the ammonium hydroxide to the 
precipitate in the test-tube just formed in (1). Shake. 
The precipitate dissolves slowly in the excess of ammonium 
hydroxide. The reaction which occurs when cadmium 
hydroxide dissolves in the excess of ammonium hydroxide 
is probably the same in principle as in the case of copper. 
Thus: 

Cd(OH) 2 + 4 NH 4 OH -> Cd(NH 3 ) 4 . (OH) 2 + 4 H 2 0. 

When this solution is treated with potassium cyanide 
solution another reaction takes place and the cadmium 

figs 1 " 1 + + 

changes from the positive ion Cd(NH 3 )4 to the negative 
ion Cd(CN) 4 . Thus: 

Cd(NH 3 ) 4 (OH) 2 +4KCN -> K 2 Cd(CN) 4 +K 2 (NH 3 ) 4 (OH) 2 . 

If sulphuretted hydrogen is now passed through this 
solution the cadmium will be again precipitated as cadmium 
sulphide. Thus: 

K 2 Cd(CN) 4 + H 2 S -> CdS 1 + 2 KCN + 2 HCN. 

Note: When any solution of a salt of copper is first 
treated with NH 4 OH in excess, and then potassium cyanide 
solution is added to it the same series of reactions as those 
just given for cadmium take place, except the last. The 
copper compound K 2 Cu(CN) 4 corresponding to the K 2 Cd- 
(CN) 4 is not precipitated by sulphuretted hydrogen. This 

makes it possible to detect copper and cadmium when both 

+ + 

are present. The blue color of the ion Cu(NH 3 ) 4 and the 
confirmatory test with K 4 Fe(CN) 6 identify copper. The 
very characteristic yellow CdS formed in the presence of 


40 


Qualitative Analysis. 


copper, which is not precipitated from the ion K 2 Cu(CN) 4 
identifies cadmium. 

Potassium cyanide is a violent poison. Great care must 
be exercised when using it. Not only is the solution 
extremely poisonous when taken internally but if acid 
comes in contact with the salt hydrocyanic acid is liberated. 
This acid is exceedingly poisonous to breathe even in very 
small amounts. The only safe plan is to keep acids away 
from this solution. Care must be taken not to discard it 
into a sink where there is acid. Allow water to run into 
the sink when discarding it and pour the cyanide directly 
into the drain. 

Conclusions. 1 . H 2 S precipitates CdS (yellow) from 
acid solutions. 

2. CdS dissolves readily in hot dilute HN0 3 . 

3. NH 4 OH precipitates Cd(OH) 2 (white). 

4. Cd(OH) 2 is soluble in excess of NH 4 OH forming 
Cd(NH 3 ) 4 (OH) 2 . 

5. KCN reacts with Cd(NH 3 ) 4 (OH) 2 forming K 2 Cd- 
(CN) 4 . 

6. H 2 S precipitates CdS from K 2 Cd(CN) 4 . H 2 S does not 
precipitate copper from K 2 Cu(CN) 4 . 


Group II— Part I. 


41 


Experiment 11. 

Title: Separation of the metals of the Sulphuretted 
Hydrogen Group: Part 1. This solution is known to con¬ 
tain Hg, Pb, Bi, Cu and Cd ions. 

1. Precipitation of the Group. Pour 5 c.c. of the solution 
containing the group into a test-tube. Add 5 drops of 
dilute nitric acid. Warm the contents of the test-tube and 
pass sulphuretted hydrogen gas through the mixture for 10 
seconds. Pour the contents of the test-tube into a beaker 
and dilute them by adding 2 test-tubes full of water to the 
beaker. Now add dilute ammonia a drop or two at a time 
until the mixture is just faintly acid when tested with litmus 
paper. Now add 4 c.c. of dilute nitric acid. These steps 
are taken in order to obtain the proper concentration of acid 
for the best results in the precipitation with sulphuretted 
hydrogen gas. Acid is frequently used in making up solu¬ 
tions for test. The ammonia neutralizes this. Now bring 
the contents of the beaker to a boil and pass sulphuretted 
hydrogen gas through it for some time. The delivery tube 
should be moved about in the mixture to insure that the 
gas saturates all parts of the solution. Two minutes will 
probably give time enough for the complete precipitation of 
all the metals as sulphides. Again bring the contents of 
the beaker to a boil and filter at once. Dilute the filtrate 
again by adding its own volume of water to it and 4 c.c. of 
nitric acid (dilute). Bring this new mixture to a boil 
again, and again pass sulphuretted hydrogen gas through it. 
If more precipitate forms pass the gas for some time. Then 
boil the contents of the beaker again and add the additional 
precipitate to that already on the filter. Continue heating 
and passing the gas until no more precipitate forms. Then 
discard the clear liquid. Wash the precipitate on the 


42 


Qualitative Analysis. 


filter paper three times with hot water from a wash bottle 
and reserve it for the next step in (2). 

2. Tests for Mercuric Mercury. Place the filter paper 
containing the precipitate reserved from (1) in an evapor¬ 
ating dish and add 10 c.c. of dilute nitric acid. Bring this 
mixture to a boil but do not allow the boiling to continue. 
A black residue, which quickly settles to the bottom of the 
dish is mercuric sulphide and indicates the presence of 
mercuric mercury. To confirm this, add 5 c.c. of stannous 
chloride to 2 c.c. of the original solution containing the 
group. Warm this mixture. If a white precipitate forms 
which turns gray upon standing the presence of mercury 
is confirmed. See experiment 6. Discard the contents of 
this test-tube as soon as a definite result is obtained. Filter 
the contents of the evaporating dish and discard the 
residue of mercuric sulphide on the filter paper. The 
filtrate contains the remaining metals of the group as 
nitrates. Reserve this for (3). 

3. Tests for Lead. Add 5 c.c. of dilute sulphuric acid to 
the filtrate reserved in (2) and boil the mixture down until 
not much more then 5 c.c. of solution remains. This 
operation is best done in a beaker. The white precipitate 
which forms is lead sulphate and indicates the presence of 
lead. This test should be confirmed as follows. Filter off 
the lead sulphate and set the filtrate aside for test in (4). 
Wash the white precipitate. Pour 5 c.c. of a mixture of a 
solution of ammonium acetate and dilute acetic acid into a 
test-tube. Warm this and pour it through the filter con¬ 
taining the lead sulphate. If all the precipitate does not 
dissolve the first time pour it through the filter again. To 
this last filtrate which contains the lead as lead acetate in 
solution add 2 drops of potassium chromate solution. The 
formation of a yellow precipitate of lead chromate confirms 
the presence of lead. 


Group II— Part I. 


43 


4. Tests for Bismuth. Neutralize the filtrate reserved 
from (3) with strong ammonium hydroxide. The mixture 
should be strongly alkaline when tested with litmus paper. 
The white precipitate which will not dissolve in the excess 
of ammonia probably indicates the presence of bismuth. 
To confirm this filter out this precipitate and set the filtrate 
aside for (5). Wash the precipitate carefully. Place a 
test-tube containing some sodium stannite solution under 
the funnel and pour 10 drops of dilute hydrochloric acid 
through the funnel into the test-tube. The formation of 
black particles of metallic bismuth at the junction of the 
two liquids in the test tube confirms the presence of bismuth. 
For details of this test see experiment 8, C, paragraph 2. 

5. Tests for Copper. If the filtrate reserved from (4) is 
a deep blue color the presence of copper is proved. If the 
color is not definite confirm the test as follows. Divide 
the solution into two equal parts. Reserve one part 
for (6). To the other part add dilute acetic acid to acid 
reaction and then a drop or two of potassium ferrocyanide 
solution. The formation of a red precipitate of copper 
ferrocyanide confirms the presence of copper . See experi¬ 
ment 9, paragraph 2. 

6. Tests for Cadmium. Test the solution reserved from 
(5) to be sure that it is strongly alkaline with ammonia. 
Then add its own volume of potassium cyanide solution 
to it and pass sulphuretted hydrogen gas through the 
mixture for 10 seconds. The formation of a finely divided 
yellow precipitate of cadmium sulphide indicates the pres¬ 
ence of cadmium. Allow the water to run in a sink free 
from acid and then discard the contents of the tube just 
used directly into the drain. Should acid come in contact 
with potassium cyanide solution hydrocyanic acid would be 
liberated. Breathing the fumes of this acid even in small 


44 


Qualitative Analysis. 


amount might prove serious. Remember that the potas¬ 
sium cyanide solution itself is a violent poison. Great care 
should he exercised in the use of this reagent. Potassium 
cyanide is used to keep the copper in solution while the 
cadmium is precipitated out by the sulphuretted hydrogen 
gas. See Experiment 10, B, 2. 

Conclusions, (a) For the explanation of each test used 
in this separation the student is referred to experiments 
6 - 10 . 

(b) The written record of this experiment should include 
explanations of every step as well as a description of the 
steps themselves. 

(c) All reactions occurring in this separation should be 
written out in equation form as a part of the written record. 
These will be found in experiments 6-10. 


Group II— Part I. 


45 


Experiment 12. 

Title: The analysis of an Unknown Solution which may 
contain any or all of the Metals of the Sulphuretted Hydro¬ 
gen Group: Part I. 

1. Directions. Proceed exactly as directed in Experi¬ 
ment 11. Where a metal is not present in the unknown 
solution the test for that ion will fail. 

2. The Written Record. In the analysis of the known 
solution in Experiment 11 the results were all recorded in 
great detail. It is not necessary to repeat this detail for 
the record of this analysis and the analyses of this group 
which follow. The brief tabular form of record given 
below will be found easy to write and will give all the facts 


The Group. 

Hg. 

Pb. 

Bi. 

Cu. 

Cd. 

Reserve a 

Residue 1 

Filtrate 1. 

Filtrate 2. 

Filtrate 3 

Filtrate 3, 

small por¬ 

is black 

Add H 2 S0 4 . 

Add NH 4 - 

is a deep 

Part 2, 
add KCN 

tion. 

HgS. 

Boil. 

OH in ex¬ 

blue color. 

Pass H 2 S. 

Indicates 

White ppt. 

cess. 

Indicates 

(caution) 

Dilute. 

mercury. 

is PbS0 4 . 

Flocculent 

copper. 

until 

Acidify. 

Add SnCl 2 

Indicates 

ppt. is 

Divide into 

colorless. 

Boil. Pass 

in excess 

lead. 

BiO(OH). 

two equal 

Pass H 2 S. 

H 2 S in ex¬ 

to portion 

Filter. 

Indicates 

parts. 

Yellow ppt. 

cess. 

of group 

Reserve 

bismuth. 

Part 1. 

is CdS. 

Filter. 

reserved. 

Filtrate 2. 

Filter. 

Acidify 

Indicates 

Discard 

White ppt. 
is HgCl. 

To white 

Reserve 

with CH 3 - 

cadmium. 

filtrate. 

ppt. add 

Filtrate 3. 

COOH. 


Wash ppt. 

Turns dark 

CHsCOO- 

Wash ppt. 

Add 1 drop 


Add HN0 3 

gray is 

NH 4 and 

Pour HC1 

K 4 Fe- 


Boil. 

Hg. 

ch 3 - 

through 

(CN) e . 


Filter. 

Confirms 

COOH. 

ppt. 

Red ppt. is 


Discard 
residue 1. 
Reserve 
filtrate 1. 

mercury. 

Warm. 

Add 
K 2 Cr0 4 . 
Yellow ppt. 
is PbCr0 4 . 
Confirms 
lead. 

Let BiCl 3 
drop into 
Na 2 Sn0 2 . 

Black par¬ 
ticles are 
Bi. 

Confirms 

bismuth. 

Cu 2 Fe- 

(CN) 6 . 

Confirms 

copper. 












46 


Qualitative Analysis. 


necessary after the pupil is familiar with the handling of 
the group. 

Note: If a metal is not found in the mixture it will be 
found satisfactory to write this fact in the proper column 
above. The column should otherwise be left blank. 


Group II— Part I. 


47 


Experiment 13. 

Title: An Analysis of an Unknown Solution which may 
contain any of the Metals of the HC1 and H 2 S—Part I 
Groups. 

1. Separation of the Metals into Groups. Follow the 
directions given in the Introduction paragraph 4 to make 
this separation. As a general rule it is better to analyze 
each group as it is removed from the solution before pre¬ 
cipitating out the next group. 

2. Analysis of the HC1 Group. Follow the directions 
given in Experiment 4 beginning with paragraph 2. Wash 
all precipitates. 

3. Analysis of the H 2 S Group: Part I. Follow the direc¬ 
tions given in Experiment 11 beginning with paragraph 2. 
Wash all precipitates. 

4. The Written Record. Write the record of this experi¬ 
ment in tabular form. Follow the directions given in 
Experiments 5 and 12. 


48 


Qualitative Analysis. 


GROUP II. 

THE SULPHURETTED HYDROGEN GROUP: PART II. 

This group contains the metals whose sulphides are 
insoluble in water and dilute acids (cold), but soluble in 
warm dilute yellow ammonium sulphide. This second facU 
gives a simple method for separating the first and second 
parts of the sulphuretted hydrogen groups. See Experi¬ 
ment 19 paragraph 3. The metals in this group are: 


Arsenic.As 

Antimony (Stibium).Sb 

Tin (Stannum).Sn 


When sulphuretted hydrogen gas is allowed to bubble * 
slowly through a hot dilute mixture of any soluble com¬ 
pounds of these metals, which has been made slightly acid 
with nitric or hydrochloric acids, these metals are precipi¬ 
tated out of the solution as sulphides: As 2 S 3 , Sb 2 S 3 , and SnS. 

Note: From some compounds of these metals they are 
precipitated as sulphides only after passing the H 2 S gas 
for a long time. Arsenic is particularly troublesome. It is 
therefore necessary, when precipitating this group, to be 
very careful to see that the precipitation of the group is 
complete.. Have the solution very dilute, boiling hot and 
pass the gas for several minutes. 





Group II— Part II. 


49 


Experiment 14. 

Title: Tests for Arsenic. Symbol As. Valence 3 and 5. 

1. Arsenic Sulphide. Pour 5 c.c. of a solution of sodium 
arsenite into a test-tube. Warm the contents of the test- 
tube and pass sulphuretted hydrogen gas through it for 10 
seconds. Empty the contents of the test-tube into a 
beaker. Fill the same test-tube with water and add this 
water to the beaker. Test the diluted solution with litmus 
paper. Unless it shows a decided acid reaction add a few 
drops of dilute nitric acid. Now bring the contents of the 
beaker to a boil and then pass sulphuretted hydrogen gas 
through them until precipitation is judged to be complete. 
The yellow precipitate formed is arsenious sulphide. The 
chemical equation for this reaction is: 

2 Na 3 As0 3 3 H 2 S As 2 S 3 { —f~ 3 Na^S 6 H 2 O. 

Filter. Discard the clear filtrate. Reserve the precipitate 
for (2). 

2. Arsenic Sulphide is Soluble in Ammonium Sulphide. 

Wash the precipitate reserved from (1) three times with 
hot water. Use a wash bottle. Remove the filter paper 
from the funnel and place that portion of the paper con¬ 
taining the precipitate in an evaporating dish and add 10 
c.c. of dilute yellow ammonium sulphide. Warm the con¬ 
tents of the dish. The arsenic sulphide will dissolve in the 
ammonium sulphide with the formation of ammonium 
thio-arsenate, also called ammonium sulpho-arsenate* 
The chemical reaction is: 


As 2 S 3 + 3 (NH 4 ) 2 S 2 -> 2 (NH 4 ) 3 AsS 4 + S. 


50 


Qualitative Analysis. 


Filter the contents of the dish into a beaker. Discard the 
residue on the filter paper. Reserve the filtrate for (3). 

3. HC1 Precipitates As 2 S 3 from (NH 4 ) 3 AsS 4 . To the 
solution of ammonium thio-arsenate in ammonium sulphide 
reserved from (2), add dilute hydrochloric acid a few drops 
at a time until the mixture, in the beaker, reacts acid when 
tested with litmus paper. The yellow precipitate produced 
is arsenious sulphide. The white precipitate is sulphur. 
The gas given off is sulphuretted hydrogen. The equation 
for this reaction is: 

2(NH 4 ) 3 AsS 4 + 6 HC1 -> As 2 S 3 | + 2 S + 3 H 2 S + 6 NH 4 C1. 

Filter the contents of the beaker. If the sulphur runs 
through the filter paper so much the better for the arsenious 
sulphide is the only substance wanted. Discard the filtrate. 
Wash the precipitate on the filter paper three times with 
hot water. Reserve this washed precipitate for (4). 

4. As 2 S 3 is Soluble in Hot (NH 4 ) 2 C0 3 Solution. Put 
that portion of the filter paper just reserved, which con¬ 
tains the precipitate of arsenious sulphide, into an evapo¬ 
rating dish. Add 10 c.c. of a 1-molar solution of ammonium 
carbonate. Now bring the contents of the dish to a boil 
and allow the boiling to continue for 10 seconds. This will 
dissolve the arsenious sulphide. The reaction for its solu¬ 
tion is: 

As 2 S 3 + 3 (NH 4 ) 2 C0 3 —> (NH 4 ) 3 As0 3 -}-(NH 4 ) 3 AsS3-}“ 3 C0 2 . 

The products formed are, in the order of the equation,— 
Ammonium arsenite, ammonium thio-arsenite, and carbon 
dioxide gas. If the solution thus formed is not clear, filter 
and reserve the clear filtrate for (5). 


Group II— Part II. 


51 


5. HC1 Precipitates As 2 S 3 from its Solution in (NH 4 ) 2 C0 3 . 

Place the filtrate reserved from (4) in a beaker and add di¬ 
lute hydrochloric acid a little at a time until the mixture, 
after stirring reacts acid. Test with litmus paper. The 
arsenic will be again precipitated as arsenious sulphide, 
yellow. 

The equation for this reaction is: 

(NH 4 ) 3 As0 3 + (NH 4 ) 3 AsS 3 + 6 HC1 -> As 2 S 3 1 

+ 6 NH 4 C1 + 3 H 2 0. 

Conclusions. 1 . H 2 S precipitates As 2 S 3 from acid solu¬ 
tions. 

2. As 2 S 3 is soluble in warm, dilute (NH 4 ) 2 S 2 . 

3. HC1 precipitates As 2 S 3 from the (NH 4 ) 2 S 2 solution (2). 

4. As 2 S 3 is soluble in warm, 1-molar (NH 4 ) 2 C0 3 solution. 

5. HC1 precipitates As 2 S 3 from the (NH 4 ) 2 C0 3 solu¬ 
tion (4). 

It should be borne in mind that the test given in (5) indi¬ 
cates the presence of arsenic only when a yellow precipitate 
forms. A yellow color alone does not indicate arsenic. 
When the quantity of arsenic present is small the precipi¬ 
tate may form only after standing. Warming tends to 
hasten the precipitation. 

Note: All arsenic compounds are very poisonous. Care 
should be exercised in handling them. 


52 


Qualitative Analysis. 


Experiment 15. 

Title: Tests for Antimony. Symbol Sb. Valence 3 
and 5. 

A. 1. Antimony Sulphide. Pour 5 c.c. of a solution of 
antimony chloride into a test-tube. Warm the contents 
of the test-tube and pass sulphuretted hydrogen gas 
through them for 10 seconds. Empty the contents of the 
test-tube into a beaker. Fill the same test-tube with water 
and add this water to the beaker. Bring this mixture to a 
boil. Now pass sulphuretted hydrogen gas through it until 
precipitation is judged to be complete. The orange colored 
precipitate which forms is antimony sulphide. The equa¬ 
tion for this reaction is: 

2 SbCl 3 + 3 H 2 S -> Sb 2 S 3 1 + 6 HC1. 

Boil the contents of the beaker and filter them at once. 
Discard the clear filtrate and reserve the precipitate on the 
filter paper for (2). 

2. Antimony Sulphide is Soluble in Ammonium Sulphide. 

Wash the precipitate reserved above three times with hot 
water. Place that part of the filter paper containing the 
precipitate in an evaporating dish. Add 10 c.c. of dilute 
yellow ammonium sulphide. Warm, but do not boil, this 
mixture. The antimony sulphide will dissolve in the 
ammonium sulphide with the formation of ammonium 
thio-stibnate, also called ammonium sulpho-antimonate. 
The equation for this reaction is: 

Sb 2 S 3 + 3 (NH 4 ) 2 S 2 -> 2 (NH 4 ) 3 SbS 4 + S. 

Filter this solution to remove the sulphur and reserve the 
clear filtrate for (3). 


Group II— Part II. 


53 


3. HC1 Precipitates Sb 2 S 3 from (NH 4 ) 3 SbS 4 . Place the 
solution reserved from (2) in a beaker and add dilute hydro¬ 
chloric acid a few drops at a time, stirring after each addi¬ 
tion of acid, until the mixture reacts acid to litmus paper. 
Avoid any large excess of the acid. The addition of this 
acid neutralizes the ammonium sulphide and again pre¬ 
cipitates the antimony as antimony sulphide (orange color). 
The equation for this reaction is: 

2 (NH 4 ) 3 SbS 4 + 6 HC1 -> Sb 2 S 3 1 

+ 6 NH 4 C1 + 3 H 2 S + 2 S. 

Filter this mixture. Wash the precipitate of antimony 
sulphide on the filter paper three times with hot water. 
Reserve this precipitate for (4). 

4. Antimony Sulphide is Soluble in Hot Cone. HC1. 
Place the part of the filter paper containing the precipitate 
reserved from (3) in an evaporating dish and add 5 c.c. of 
concentrated hydrochloric acid. Boil this mixture gently 
until the antimony sulphide is dissolved. Dilute the solu¬ 
tion thus formed with 10 c.c. of water and filter it. This 
clear solution contains the antimony as antimony chloride. 
The reaction for its formation is: 

Sb 2 S 3 + 6 HC1 -> 2 SbCl 3 + 3 H 2 S. 

Reserve this solution for (5). 

5. An Electrolytic Test for Antimony. Boil the solution 
of antimony chloride down to 5 c.c. in an evaporating dish. 
This will concentrate the solution and expel the excess 
hydrochloric acid. Place three drops of this solution on a 
piece of platinum foil. Stand a small piece of zinc in this 

5 


54 


Qualitative Analysis. 


liquid touching the foil. In a few moments a dark stain 
(nearly black) of metallic antimony will be deposited on the 
platinum foil under the zinc. The stain may be removed 
by heating the platinum bright red when the antimony 
will be volatilized, or it may be turned to a white powder 
(composition variable with the strength of the acid used) 
by treating it with dilute nitric acid. The equation for 
the formation of this stain of metallic antimony is: 

2 SbCl 3 + 3 Zn -> 3 ZnCl 2 + 2 Sb. 

Continue boiling the solution of antimony chloride down 
with a low flame until not more than a few drops remain. 
Reserve this liquid for (6). 

6. Reaction of Antimony Chloride with Water. Fill a 

test-tube nearly full of water. To this add not more than 
two drops of the concentrated solution of antimony chloride 
reserved from (5). If this solution is very concentrated a 
white flocculent precipitate of antimony oxy-chloride will 
form. The equation for this reaction is: 

SbCl 3 + H 2 0 -> SbOCl 1 + 2 HC1. 

If this precipitate forms, pour out half the contents of the 
test-tube and add to the remainder about 5 c.c. of a solution 
of tartaric acid. Shake the mixture. The antimony oxy¬ 
chloride will at once dissolve. The equation for this solu¬ 
tion is: 

2 SbOCl + (CH.OH) 2 .(COOH) 2 

-> (CH. OH) 2 . (COOSbO) 2 + 2HC1. 

B. 1 . Reaction of Antimony Chloride with Water. In 

case the test in (6) fails, add two drops of “ Butter of 


Group II —Part II. 


55 


Antimony” (a very concentrated solution of antimony 
chloride made by distillation) to a test-tube full of water. 
The equation for this reaction is given in (6). Confirm 
this test with tartaric acid as explained in (6). 

Conclusions. 1 . H 2 S precipitates Sb 2 S 3 from acid solu¬ 
tions. 

2. Sb 2 S 3 dissolves in (NH 4 ) 2 S 2 forming (NH 4 ) 3 SbS 4 . 

3. (NH 4 ) 3 SbS 4 is decomposed by dilute HC1 giving Sb 2 S 3 
again. 

4. Sb 2 S 3 dissolves in hot cone. HC1 forming SbCl 3 . 

5. Zn displaces Sb from SbCl 3 forming deposit of Sb 
on Pt. 

6. H 2 0 forms SbOCl with SbCl 3 . SbOCl dissolves in 
(CH.OH) 2 .(COOH) 2 . 


56 


Qualitative Analysis. 


Experiment 16. 

Title: Tests for Tin. Symbol Sn. Valence 2 and 4. 

A. 1 . Stannous Sulphide. Pour 5 c.c. of a solution of 
tin chloride into a test-tube. Warm the contents of the 
test-tube and pass sulphuretted hydrogen gas through it 
for 10 seconds. Empty the contents of thetest-tube into 
a beaker. Fill the same test-tube with water and add 
this to the beaker. Test this solution with litmus paper. 
Unless it is decidedly acid add nitric or hydrochloric acid, 
a few drops at a time, until it is. Bring this mixture to a 
boil. Now pass sulphuretted hydrogen gas through it 
until precipitation is judged to be complete. The brown 
precipitate which forms is stannous sulphide. The equa¬ 
tion for this reaction is: 

SnCl 2 + H 2 S -> SnS 1 + 2 HC1. 

Bring the contents of the beaker to a boil. Filter. Discard 
the clear filtrate. Wash the precipitate three times with 
hot water. Reserve this precipitate for (2). 

2. Stannous Sulphide is Soluble in Ammonium Sulphide. 
Place that portion of the filter paper containing the pre¬ 
cipitate, reserved form (1), in an evaporating dish and add 
10 c.c. of dilute ammonium sulphide (yellow). Warm this 
mixture gently. Stir it during the warming. The stannous 
sulphide dissolves in the ammonium sulphide forming 
ammonium thiostannate, also called ammonium sulpho- 
stannate. The equation for this reaction is: 

SnS + (NH 4 ) 2 S 2 -> (NH 4 ) 2 SnS 3 . 

Reserve this clear solution for (3). If not clear it should be 
filtered. Discard any residue on the filter paper. 


Group II —Part II. 


57 


3. HC1 Precipitates Stannic Sulphide from (NH 4 ) 2 SnS 3 . 

Pour the clear solution reserved from (2) into a beaker and 
add dilute hydrochloric acid, a few drops at a time, stirring 
after each addition of the acid until the mixture reacts acid 
with litmus paper. The yellow precipitate which forms is 
stannic sulphide. Some white sulphur will also form at the 
same time from the decomposition of the excess ammonium 
sulphide by the acid. The equation for this reaction is: 

(NH 4 ) 2 SnS 3 + 2 HC1 -> SnS 2 J + 2 NH 4 C1 + H 2 S. 

Filter the contents of the beaker and wash the precipitate 
three times with hot water. Reserve this washed precipi¬ 
tate only for the test in (4). 

4. Stannic Sulphide is Soluble in Hot Cone. HC1. Place 
that portion of the filter paper containing the precipitate 
in an evaporating dish. Add 5 c.c. of concentrated hydro¬ 
chloric acid. Bring this mixture to a boil and continue to 
boil it slowly over a low flame until the stannic sulphide is 
dissolved. The compound formed is stannic chloride. The 
equation for this reaction is: 

SnS 2 + 4 HC1 -> SnCl 4 + 2 H 2 S. 

Dilute the contents of the evaporating dish with 10 c.c. of 
water and filter them into a beaker or other evaporating 
dish. Reserve this clear filtrate for (5). 

5. Reduction of SnCl 4 to SnCl 2 . Boil the solution of 
stannic chloride, reserved from (4) down to about 5 c.c. 
This will expel the excess hydrochloric acid and concentrate 
the solution. Add three or four small iron nails to this 
solution and allow the effervescence which results to con¬ 
tinue for 10 or 15 minutes. This will reduce the stannic 


58 Qualitative Analysis. 

chloride to stannous chloride. The equation for this reac¬ 
tion is: 

SnCl 4 + Fe -> SnCl 2 + FeCl 2 . 

Filter the mixture of stannous chloride and ferrous chloride 
solutions and to this filtrate add not more than two or three 
drops of a solution of mercuric chloride. The white pre¬ 
cipitate which forms is mercurous chloride. The reac¬ 
tion is: 

SnCl 2 + 2 HgCl 2 -> 2 HgCl [ + SnCl 4 . 

Upon standing or slight heating this precipitate turns dark 
gray. This is due to the further reduction of the mercurous 
chloride to metallic mercury. The equation is: 

2 HgCl + SnCl 2 -> 2 Hg l + SnCl 4 . 

Note: This test is very characteristic. It was also 
used to identify mercuric mercury. See Experiment 6. In 
this case stannous chloride was the reagent. It was added 
to the mercury solution in excess. In this case mercuric 
chloride is the reagent and it is added in very small amount 
in order that the tin solution may still be in excess. 

B. 1. The Reaction of HgCl 2 with SnCl 2 . The test just 
described in A. (5) above may be made as a separate test 
by adding a few drops of mercuric chloride solution to 5 c.c. 
of stannous chloride reagent. In this case the same chemi¬ 
cal reactions, of course, occur. 

Conclusions. 1 . H 2 S precipitates SnS from acid solu¬ 
tions. 

2. SnS is soluble in dilute (NH 4 ) 2 S 2 as (NH 4 ) 2 SnS 3 . 

3. SnS 2 is precipitated from the (NH 4 ) 2 SnS 3 solution 
by HC1. 


Group II —Part II. 


59 


4. SnS 2 is soluble in cone. HC1 forming SnCl 4 . 

5. SnCl 4 is reduced by Fe to SnCl 2 . 

6. HgCl 2 precipitates HgCl from SnCl 2 solutions. 
(White.) 

7. SnCl 2 in excess further reduces HgCl to Hg. 


60 


Qualitative Analysis. 


Experiment 17. 

Title: Separation of the Metals of the Sulphuretted 
Hydrogen Group: Part 2. This solution is known to con¬ 
tain As, Sb, and Sn ions. 

1. Precipitation of the Group. Pour 5 c.c. of the solu¬ 
tion containing the group into a test-tube. Warm this 
solution and pass sulphuretted hydrogen gas through it for 
10 seconds. Pour the contents of the test-tube into a 
beaker. Fill the same test-tube twice with water and add 
both test-tubes full to the beaker. Also add 2 c.c. of dilute 
hydrochloric acid to the contents of the beaker and then 
heat them to boiling. Now pass sulphuretted hydrogen 
gas through the mixture until precipitation is judged to be 
complete. Use a slow stream of the gas and stir the mixture 
constantly with the end of the gas delivery tube. Again 
bring the contents of the beaker to a boil and filter them 
at once. To the clear filtrate add a third test-tube full of 
water. Boil again and then pass more sulphuretted hydro¬ 
gen gas through this liquid. If more precipitate forms add 
it to that already on the filter. Continue in this way 
diluting and heating and passing the gas until no more 
precipitate forms. If the work has been carefully done the 
precipitation should be complete the first time the gas is 
passed through the diluted solution. Discard the last clear 
filtrate. Wash the precipitate on the filter paper three 
times with hot water. Reserve this washed precipitate for 
(2). It contains the sulphides of arsenic, antimony and 
tin. For the reactions which occur during precipitation 
and the subsequent separation of the group consult Experi¬ 
ments 13-15. 

2. The Test for Arsenic. Puncture the bottom of the 
filter paper containing the sulphides As 2 S 3 , Sb 2 S 3 , and SnS 


Group II— Part II. 


61 


with a small splinter. Pour a test-tube full of a 1-molar 
solution of ammonium carbonate through the filter. Pour 
the same liquid through the filter again and continue to 
repeat this process until practically all the precipitate has 
been washed through with the ammonium carbonate solu¬ 
tion into a beaker. Discard the filter paper. Bring the 
contents of the beaker to a boil and continue the boiling 
for 10 seconds. Now filter the contents of the beaker. The 
filtrate will*contain the arsenic, and the antimony and tin 
will remain on the filter paper. Reserve this residue for (3). 
Add dilute hydrochloric acid a little at a time to the clear 
filtrate. Stir after each addition of the acid. Continue in 
this way until the mixture reacts acid to litmus. A floccu- 
lent, light yellow precipitate which forms is As 2 S 3 , and 
indicates arsenic. 

3. The Test for Antimony. Wash the precipitate on the 
filter paper, reserved from (2), three times with hot water. 
Place as much of this filter paper as is covered with pre¬ 
cipitate in an evaporating dish and add 5 c.c. of concen¬ 
trated hydrochloric acid. Boil this mixture over a low 
flame until all but the filter paper, and possibly a little 
sulphur, is dissolved. Dilute this solution with 20 c.c. of 
water and filter it. Discard the residue on the filter paper. 
The clear filtrate contains the antimony and the tin. Boil 
this filtrate down in an evaporating dish until not much 
more than 5 c.c. remains. This will expel any excess 
hydrochloric acid and concentrate the solution. Place 
three drops of this concentrated solution on a piece of 
platinum foil and stand a small piece of metallic zinc in this 
liquid. If a very dark stain forms on the platinum under 
the zinc, it is metallic antimony and indicates the presence 
of antimony. (In the absence of platinum foil this test 
may be omitted.) To the balance of the solution add three 


62 


Qualitative Analysis. 


small iron nails. Heat this mixture until a brisk effer¬ 
vescence of gas occurs. Allow this action to continue for 
15 minutes without further heating. This time is necessary 
to reduce any tin present to the stannous state. If a 
number of black particles appear in the liquid they are 
probably antimony. To confirm this point filter the 
mixture. Reserve the filtrate for the test for tin in (4). 
Make a small hole in the bottom of the filter paper. Pour 
10 c.c. of hot tartaric acid solution, to which 2 drops of 
dilute nitric acid have been added, through this filter over 
the nails. Repeat the pouring until all the black particles 
have been washed through with the acid. If these have 
not dissolved bring the liquid to a boil, and then pass 
sulphuretted hydrogen gas through it. If an orange yellow 
precipitate forms it is Sb 2 S 3 , and indicates antimony. 

4. The Test for Tin. To the filtrate reserved from (3) 
add not more than 3 drops of mercuric chloride solution. 
A white precipitate which forms is HgCl, and indicates tin. 
If this precipitate turns dark gray upon standing or slight 
heating the gray color is due to Hg formed by the further 
reduction of the HgCl by the stannous chloride present in 
the solution. This last test confirms the presence of tin. 

Conclusions, (a) For the explanation of each test in 
this separation the student is referred to Experiments 14-16. 

(6) The written record of this experiment should include 
explanations of every step as well as a description of the 
steps themselves. 

(c) All reactions occurring in this separation should be 
written out in equation form as a part of the written record. 
These will be found in Experiments 14-16. 


Group II— Part II. 


63 


Experiment 18. 

Title: Analysis of an Unknown Solution. This Solution 
may contain any or all of the Metals of “The Sulphuretted 
Hydrogen Group”: Part II. 

1. Directions. Follow the directions given in Experi¬ 
ment 17 exactly. 

2. The Written Record. Record the result of your anal¬ 
ysis in tabular form as shown in the table below. When a 
metal is not found in a solution its column should be left 
blank or simply the words “Not found” inserted in the 
column. 


The Group. 

Aa. 

Sb. 

Sn. 

(NH 4 ) 2 S 2 filtrate 

Filtrate 1 

Residue 1 

Filtrate 2, 

+ 

+ 

+ 

part 2 

dilute HC1 

Dilute HC1 in 

Cone. HC1. 

+ 

gives precipi¬ 

excess. 

Boil, dilute, fil¬ 

Fe. 

tate As 2 S 3 , Sb 2 - 

Yellow ppt. is 

ter, concen¬ 

Filter. 

S 3 , SnS, if these 

As 2 S 3 . 

trate. 

Filtrate 3 

metals are pres¬ 
ent. 

+ 

(NH 4 ) 2 C0 3 . 
Boil, filter. 
Reserve: 

Residue 1, 
Filtrate 1. 

Indicates arsenic. 

Filtrate 2 (few 
drops) 

+ 

Zn & Pt. 
Black stain is 
Sb, indicates 
antimony. 

+ 

2 drops HgCl 2 . 
White ppt. is 
HgCl. 

Gray ppt. is 
Hg. 

Indicates tin. 


Conclusions: (a) The student should constantly refer 
back to the Experiments giving the tests for the individual 
metals in order that the details of these tests shall be 
followed. 

(i b ) While it is not necessary to write the chemical equa¬ 
tions involved in each reaction every time a separation is 
carried out, nevertheless the student should be able to do 
this. When this is not possible the student should form 









64 


Qualitative Analysis. 


the habit of looking these up and in this way constantly 
reviewing them. Qualitative work done mechanically 
without a detailed knowledge of the reasons for, and the 
results of, all steps, is worthless. 

(c) If the student’s report on an analysis is incorrect, 
this mixture should be re-analyzed until the result is correct. 

(d) This is a good point at which to analyze a number of 
unknown solutions until all separations and tests thus far 
considered can be carried out by the pupil without reference 
to the printed directions. Experiment 19 is a good example 
of the type of practice work that should be used at this 
point. 


Group II— Part II. 


65 


Experiment 19. 

Title: Analysis of an Unknown Solution which may 
contain any of the Metals of the HC1 Group, the H 2 S 
Group: Part I and the H 2 S Group: Part II. 

1. Separation into Groups. Follow the directions given 
in the “Introduction: paragraph 4.” 

2. Analysis of the HC1 Group. Follow the directions 
given in Experiment 4 beginning with paragraph 2. 

3. Separation of the H 2 S Group into Parts I and II. 
Wash the whole precipitate produced by sulphuretted 
hydrogen three times with hot water on the filter paper. 
Place as much of the filter paper as is covered with precipi¬ 
tate in an evaporating dish and add to it 20 c.c. of dilute 
ammonium sulphide. Warm but do not boil the contents 
of the dish. Allow this mixture to stand two minutes 
stirring it from time to time. At the end of this time filter 
the contents of the dish. Wash the residue on the filter 
paper with hot water until the wash water is colorless and 
then reserve this residue for the analysis of Part I. 

To the ammonium sulphide filtrate, which has been placed 
in a beaker add dilute hydrochloric acid until the mixture 
reacts acid to litmus after thorough stirring. Bring this 
mixture to a boil and filter it hot. Wash this precipitate 
three times with hot water and then reserve it for the 
analysis of Part II. 

4. Analysis of Part I. Follow the directions given in 
Experiment 11 beginning with paragraph 2. 

5. Analysis of Part II. Follow the directions given in 
Experiment 17 beginning with paragraph 2. 

6. The Written Record. Record the results of this 
analysis in tabular form as suggested in Experiments 5, 
12 and 18. 


66 


Qualitative Analysis. 


GROUP III. 

THE AMMONIUM HYDROXIDE GROUP. 

This group contains the metals whose hydroxides are 
insoluble in a hot alkaline (with ammonium hydroxide) 
solution to which a considerable amount of ammonium 
chloride has been added. The metals in this-group are: 


Chromium.Or 

Aluminum.A1 

Iron (Ferrum).Fe 


The ammonium chloride used in precipitating this group 
is very important. The large number of ammonium ions 
which it produces in the solution forces the ions of the 
metals of this group out of solution as hydroxides. The 
hydroxyl (OH) radical is of course furnished by the am¬ 
monium hydroxide used to precipitate the group. 





Group III. 


67 


Experiment 20. 

Title: Tests for Chromium. Symbol Cr. Valence 2, 
3 and 6. 

A. 1 . A Partial Precipitation of Chromium Hydroxide. 

Pour 5 c.c. of a solution of chromic nitrate into a test-tube 
and add dilute ammonium hydroxide in excess. A gelati¬ 
nous bluish green or gray precipitate of chromic hydroxide 
will form. The equation for this reaction is: 

Cr(N0 3 ) 3 + 3 NH 4 OH -> Cr(OH) 3 1 + 3 NH 4 N0 3 . 

Shake the contents of the test-tube for a few moments. 
If the odor of ammonia is not strongly apparent add two 
cubic centimeters more of dilute ammonium hydroxide 
and shake again. Filter the contents of the test-tube, 
which should be cold, and observe the pink violet color of 
the clear filtrate. This color is due to a small amount of 
the chromic hydroxide dissolved in the excess of the am¬ 
monium hydroxide. Now boil this clear pink filtrate for a 
few moments. It will quickly become cloudy due to the 
precipitation of the dissolved chromic hydroxide by the 
heat. 

2. A Complete Precipitation of Chromium Hydroxide. 

Pour another 5 c.c. of chromic nitrate solution into a test- 
tube and add to it its own volume of ammonium chloride 
solution. Bring this mixture to a boil and then add an 
excess of ammonium hydroxide to it. The precipitate of 
chromic hydroxide will again form as in (1). Filter this 
precipitate from the clear liquid. This time the filtrate 
will be colorless, showing that the ammonium chloride and 
the heat together cause the complete precipitation of the 
chromium as chromic hydroxide. This is an important 


68 


Qualitative Analysis. 


point in the analysis of this group. Wash the precipitate 
on the filter paper and reserve it for (3). 

3. Sodium Dioxide Dissolves Chromium Hydroxide. 

Puncture the point of the filter paper reserved from (2) 
and wash the precipitate into an evaporating dish with a 
wash bottle. Use only a small amount of water. Not 
more than 10 c.c. Put 2 grams of sodium dioxide (esti¬ 
mated) on a piece of filter paper. Quickly add this to the 
precipitate and water in the evaporating dish. Run water 
at once upon the sheet of filter paper used to convey the 
podium dioxide to the evaporating dish or this paper is 
liable to take fire spontaneously. Caution must be used 
in handling sodium dioxide. The need for this is two-fold. 
When moisture comes in contact with this chemical so much 
heat is generated that the danger from fire is considerable. 
If the paper used is thoroughly wet before discarding it this 
danger will be removed. The eyes must also be guarded when 
the sodium dioxide is put into water as a little of the mixture 
may fly. Should this come in contact with the eye the result 
would be serious. Bring the contents of the evaporating 
dish to a boil and continue the boiling until effervescence 
ceases. The sodium dioxide converts the chromium 
hydroxide into sodium chromate. This probably occurs in 
three steps as follows: 

Na20 2 + H 2 0 —> 2 NaOH + O, 

Cr(OH) 3 + NaOH -> NaCr0 2 + 2 H 2 0, 

2 NaCr0 2 + 2 Na 2 0 2 + H 2 0 + 0 -> 2 Na 2 Cr0 4 + 2 NaOH. 

Pour this liquid into a test-tube when its strong yellow 
color may be more clearly seen. The yellow color of 


Group III. 


69 


sodium chromate formed in this way is a very characteristic 
test for this metal. 

Conclusions. 1 . NH 4 OH precipitates Cr(OH) 3 com¬ 
pletely from hot solutions of chromium salts containing an 
excess of NH 4 C1. 

2. When Cr(OH) 3 is boiled with Na 2 0 2 it is converted 
into yellow Na 2 Cr0 4 . NaCr0 2 is sodium chromite. 


6 


70 


Qualitative Analysis. 


Experiment 21. 

Title : Tests for Aluminum. Symbol Al. Valence 3. 

A. 1 . A Partial Precipitation of Aluminum Hydroxide. 

Pour 5 c.c. of a solution of aluminum nitrate into a test- 
tube and add dilute ammonium hydroxide. Note the 
flocculent white precipitate of aluminum hydroxide which 
forms. The reaction is as follows: 

A1(N0 3 ) 3 + 3 NH 4 OH -> Al(OH) 3 | + 3 NH 4 N0 3 . 

Now add a considerable excess of the ammonium hydroxide 
and shake the contents of the test-tube vigorously. A con¬ 
siderable amount of the aluminum hydroxide will dissolve 
in the excess of the ammonium hydroxide. Filter the 
contents of the test-tube. To the clear filtrate add its 
own volume of ammonium chloride solution and bring the 
mixture to a boil. Upon boiling the dissolved aluminum 
hydroxide will be re-precipitated. Long boiling produces 
the same result without the addition of the ammonium 
chloride. 

2. A Complete Precipitation of Aluminum Hydroxide. 

Pour 5 c.c. of aluminum nitrate solution into a test-tube 
and to it add its own volume of ammonium chloride solution. 
Boil this mixture and then add to it some dilute ammonium 
hydroxide. If an excess of the ammonium hydroxide is 
added the precipitation of the aluminum hydroxide will be 
complete. To prove this filter the mixture in the test-tube. 
To the filtrate add more ammonium chloride solution and 
boil the mixture for some time. No more aluminum 
hydroxide will be precipitated, showing that in the presence 
of ammonium chloride and heat the precipitation of 
aluminum hydroxide by ammonium hydroxide is complete. 


Group III. 


71 


B. 1. Sodium Hydroxide Precipitates Aluminum Hydrox¬ 
ide Soluble in Excess. Pour 5 c.c. of aluminum nitrate 
solution into a test-tube and to it add a solution of sodium 
hydroxide a drop or two at a time. This will produce a 
white flocculent precipitate of aluminum hydroxide. The 
reaction is: 

A1(N0 3 ) 3 + 3 NaOH -> Al(OH), 1 + 3 NaN0 3 . 

If an excess of sodium hydroxide is now added and the 
contents of the test-tube shaken the aluminum hydroxide 
precipitate will completely dissolve in the excess of the 
sodium hydroxide with the formation of sodium aluminate. 
The reaction is: 

Al(OH), + 3 NaOH -> Na 3 A10 3 + 3 H 2 0. 

Reserve this clear solution. 

2. Sodium Dioxide Dissolves Aluminum Hydroxide. 

To the clear solution just reserved add its own volume of 
ammonium chloride solution and boil. Under these con¬ 
ditions the aluminum hydroxide is completely re-pre¬ 
cipitated. Filter off this precipitate and wash it thor¬ 
oughly. Now puncture the apex of the filter cone and 
wash the aluminum hydroxide through into an evaporating 
dish. Use very little water: not over 10 c.c. To the 
contents of the dish add 2 grams (estimated) of sodium 
dioxide and bring the mixture to a boil. Boil until effer¬ 
vescence ceases. This will completely dissolve the alum¬ 
inum hydroxide. The action is the same as in (1). When 
sodium dioxide reacts with water sodium hydroxide and 
oxygen are formed. Thus: 


Na 2 0 2 "b H 2 0 2 NaOH -f- 0. 


72 


Qualitative Analysis. 


This sodium hydroxide dissolves the aluminum hydroxide 
with the formation of sodium aluminate just as it did when 
added in excess in (1). From the solution just formed the 
aluminum hydroxide may be again precipitated by the 
addition of its own volume of ammonium chloride solution 
and boiling. Try this. 

Note: In handling sodium dioxide observe the same pre ¬ 
cautions given in Experiment 18 . 

Conclusions. 1 . NH 4 OH precipitates Al(OH) 3 . 

2. Al(OH) 3 is somewhat soluble in excess of cold NH 4 OH. 

3. Al(OH) 3 is re-precipitated upon long boiling or by 
bringing to a boil in the presence of an excess of NH 4 C1. 

4. NaOH precipitates Al(OH) 3 completely soluble in 
excess forming Na 3 A10 3 . 

5. Na 2 0 2 and H 2 0 dissolve Al(OH) 3 . This is due to the 
NaOH formed by the action of the Na 2 0 2 upon the H 2 0. 

6. NH 4 C1 and heat reprecipitate the Al(OH) 3 from the 
Solution of Na 3 A10 3 formed in (5). 


Group III. 


73 


Experiment 22. 

Title: Tests for Iron. Symbol Fe. Valence 2 and 3 . 

A. 1 . Ferrous Ions are not Completely Precipitated by 

NH 4 OH. Pour 5 c.c. of ferrous sulphate solution into a 
test-tube and add a few drops of ammonium hydroxide. 
Note the light green precipitate of ferrous hydroxide which 
forms. The reaction is: 

FeS0 4 + 2 NH 4 OH -> Fe(OH) 2 1 + (NH 4 ) 2 S0 4 . 

Ferrous iron is not completely precipitated by ammonium 
hydroxide. 

2. Ferric Ions are Completely Precipitated by NH 4 OH. 

Pour 5 c.c. of ferric chloride solution into a test-tube and 
add a few drops of ammonium hydroxide. Note the 
formation of a bulky brown precipitate of ferric hydroxide. 
The reaction is: 

FeCl 3 + 3 NH 4 OH -> Fe(OH) 3 1 + 3 NH 4 C1. 

Ferric hydroxide is not soluble in excess of ammonium 
hydroxide. Ferric iron is completely precipitated by am¬ 
monium hydroxide. Filter off the precipitate of ferric 
hydroxide and wash it thoroughly with water on the filter 
paper. Place a test-tube under the funnel and then pour a 
few drops of dilute hydrochloric acid over the precipitate 
on the paper. Note how readily ferric hydroxide dissolves 
in this acid. The reaction is: 

Fe(OH ) 3 + 3 HC1 -> FeCl 3 + 3 H 2 0. 

B. 1 . The Sulphocyanide Test for Iron. Pour 5 c.c. of 
ferric chloride solution into a test-tube and add a few drops 


74 


Qualitative Analysis. 


of potassium sulpho-cyanide solution. A red color (not 
precipitate) is produced due to the formation of ferric 
sulpho-cyanide. The reaction is: 

FeCl 3 + 3 KCNS -> Fe(CNS) 3 + 3 KCL 

Bring the contents of the test-tube to a boil. Boiling does 
not effect the red color unless the heating is long continued. 

2 . The Sulphocyanide Test for Iron Confirmed. Pour 
5 c.c. of dilute nitric acid into a test-tube and to this add a 
few drops of potassium sulpho-cyanide. A red color identi¬ 
cal in appearance to that formed in (1) will be produced. 
Bring this mixture to a boil. The red color is dissipated. 
When using the potassium sulpho-cyanide test for iron the 
mixture should always be brought to a boil otherwise the 
color formed when nitric acid is present might be mistaken 
for iron. 

C. The Reduction of Ferric Compounds by H 2 S. Pour 
10 c.c. ferric chloride solution into a test-tube and pass a 
slow stream of sulphuretted hydrogen gas through it for 
two minutes. The action of the sulphuretted hydrogen is 
as follows: 

2 FeCl 3 + H 2 S -> 2 FeCl 2 + 2 HC1 + S. 

Filter off the sulphur and note that the solution is now 
nearly colorless instead of yellow or brown. Boil this 
solution to expel the H 2 S. To this clear filtrate add a few 
drops of dilute ammonium hydroxide. The precipitate 
which forms is green showing the presence of ferrous iron. 
Compare A (1) of this experiment. 

D. The Oxidation of Ferrous Compounds by HN0 3 . 
Pour 10 c.c. of ferrous sulphate solution into an evaporating 
dish. Bring this liquid to a boil and then add concentrated 


Group III. 


75 


nitric acid to the contents of the dish. Continue boiling 
and adding the acid until no further change occurs to the 
mixture in the dish. The reactions which occur are: 

2 HN0 3 + A -> 2 NO + H 2 0 + 3 0, 

6 FeS0 4 + 3 0 -> 2 Fe 2 (S0 4 ) 3 + Fe 2 0 3 . 

Adding these two partial equations we have: 

6 FeS0 4 + 2 HN0 3 + A -> 2 Fe 2 (S0 4 ) 3 

■T Fe 2 0 3 + 2 NO -T H 2 0. 

The iron trioxide now dissolves in the excess of nitric acid 
used as follows: 

Fe 2 0 3 + 6 HN0 3 -> 2 Fe(N0 3 ) 3 + 3 H 2 0. 

Hence the ferrous sulphate has been oxidized by the nitric 
acid in the presence of heat to a mixture of ferric sulphate 
and ferric nitrate. To show this pour the contents of the 
evaporating dish into a test-tube and add an excess of 
ammonium hydroxide. The formation of a brown pre¬ 
cipitate of ferric hydroxide insoluble in the excess of the 
ammonium hydroxide, shows that the iron is now in the 
ferric state. Compare A (2) of this experiment. 

Conclusions. 1. NH 4 OH precipitates Fe(OH) 2 , green, 
from ferrous solutions, but not completely. 

2. NH 4 OH precipitates Fe(OH) 3 (brown) from ferric 
solutions. 

3. Fe(OH) 3 is not soluble in excess of NH 4 OH. It dis¬ 
solves in HC1. 

4. KCNS gives no color with ferrous solutions. 


76 


Qualitative Analysis. 


5 . KCNS gives a dark red color with ferric solutions. 
This color is not removed by brief boiling. 

6 . KCNS gives a dark red color with solutions containing 
nitric acid. This color is removed by boiling. 

7. H 2 S reduces ferric compounds to ferrous compounds. 

8 . HN0 3 and heat oxidize ferrous compounds to ferric 
compounds. 


Group III. 


77 


Experiment 23. 

Title: Separation of the Metals of the Ammonium 
Hydroxide Group. This solution is known to contain Cr, 
A1 and Fe ions. 

1. Precipitation of the Group. Pour 10 c.c. of the solu¬ 
tion containing the group into a beaker. Boil this solution 
slowly and from time to time during the boiling add con¬ 
centrated nitric acid a drop or two at a time. Continue 
in this manner boiling and adding the acid until the solution 
assumes a straw color or at least until there is no further 
change of color. This treatment will oxidize any ferrous 
iron present to the ferric state and thus insure its complete 
precipitation in the next step. Now add 10 c.c. of strong 
ammonium chloride solution to the contents of the beaker 
and then ammonium hydroxide (dilute) until precipitation 
is judged to be complete. The hot solution should smell 
strongly of ammonia. Now boil the mixture for a minute 
and filter immediately hot. Try the clear filtrate with a 
drop more of ammonium hydroxide. If no more precipi¬ 
tate forms discard it. Wash the precipitate on the filter 
paper three time with hot water. Reserve this precipitate 
for (2). It contains the hydroxides of chromium, aluminum 
and ferric iron. 

2. The Test for Chromium. Puncture the apex of the 
filter paper reserved form (1) and wash the precipitate 
through this opening into an evaporating dish. Do not use 
more than 10 c.c. of water for this purpose. Add 2 grams 
of sodium dioxide to the contents of the dish. This amount 
may be estimated approximately. Use caution in handling 
sodium dioxide. (See Experiment 18.) Boil the contents 
of the dish slowly until effervescence ceases. Dilute the 
contents of the dish with 10 c.c. of water and filter at once, 


78 


Qualitative Analysis. 


into a beaker. A bright yellow filtrate is due to the 
presence of sodium chromate and indicates chromium. 
Reserve both the residue on the filter paper and the filtrate. 

3. The Test for Aluminum. To the yellow filtrate re¬ 
served from (2) add its own volume of a strong solution of 
ammonium chloride. Heat the contents of the beaker and 
note the formation of a white flocculent precipitate of 
aluminum hydroxide. This precipitate indicates the pres¬ 
ence of aluminum. 

Since the presence of silicon or lead (from the glass) will 
give a similar precipitate at this point the test for aluminum 
should be confirmed .as follows. Filter off the aluminum 
hydroxide precipitate (supposedly) and wash this on the 
filter paper free from sodium chromate. Dissolve the 
washed precipitate by repeatedly pouring 5 c.c. of warm 
dilute nitric acid through the filter. To this solution add 
10 drops of a 1 per cent solution of cobalt nitrate (Co- 
(N0 3 ) 2 ). Evaporate this mixture nearly to dryness in an 
evaporating dish. Add two drops of water to the cooled 
residue. Soak this up with a little piece of filter paper. 
Ignite the filter paper on a piece of platinum foil. When 
the carbon of the paper has been burned away the forma¬ 
tion of a blue residue, which is probably Co(A10 2 )2 confirms 
aluminum. If the residue is black it may be due to the 
use of too large a quantity of the cobalt nitrate: in this 
case the test should be repeated with a smaller proportion 
of the cobalt nitrate. 

4. The Test for Iron. Wash the precipitate on the filter 
paper reserved in (1). Pour dilute hydrochloric acid, which 
has been warmed through the filter so that it comes in 
contact with all the residue of ferric hydroxide. This will 
dissolve the ferric hydroxide. To this filtrate add a few 
drops of a solution of potassium sulpho-cyanide. The 


Group III. 


79 


formation of a red color indicates iron. Bring this red 
solution to a boil: if the color remains the presence of 
iron is confirmed. 

Conclusions, (a) For the explanation of each step 
used in this separation as weh as the chemical equations 
involved in the reactions the student is referred to Experi¬ 
ments 18-20. 

(6) The written record should include the explanation of 
each step taken, including the chemical equations involved, 
as well as the description of the steps themselves. 


80 


Qualitative Analysis. 


Experiment 24. 

Title: Analysis of an Unknown Solution which may 
contain any or all of the Metals of the Ammonium Hydrox¬ 
ide Group. 

1. Directions. Follow the directions given in Experi¬ 
ment 23. 

2. The Written Record. The tabular form of record 
shown below should be used in writing up this experiment. 


The Group. 

Cr. 

Al. 

Fe. 

10 c.c. of the un¬ 

Ppt. 1 

Filtrate 2 

Residue 1. 

known solution 

4* 

+ 

Dissolve in 5 

+ 

10 c.c. of H 2 0 

10 c.c. NH 4 CI 

c.c. dilute 

Boiling 

+ 

+ 

HC1 

+ 

2 gm. Na 2 0 2 

Boiling. White 

4* 

A few drops of 

+ 

flocculent ppt. 

KCNS. 

cone. HN0 3 

Boiling. 

is Al(OH) 3 . 

Red color is 

4~ 

Filter. 

Indicates alum¬ 

Fe(CNS) 3 . 

Boiling 

Yellow filtrate 

inum. 

Indicates iron 

+ 

due to Na 2 Cr0 4 

Filter. Wash 

4" 

10 c.c. NH 4 C1. 

Indicates 

ppt. dissolve in 

Boiling. 

NH 4 OH in excess. 

chromium. 

dilute HN0 3 

If color re¬ 

Boil. Filter. 

Reserve: 

(warm) 

mains, iron is 

Wash ppt. 
Reserve ppt. 1. 
Discard 
filtrate 1 . 

Filtrate 2. 
Residue 1. 

4* 

Very little 
Co(N0 3 ) 2 . 

Boil to dryness 
+ 

2 drops of H 2 0 
+ 

Filter paper. 
Burn. Blue ash 
confirms 
aluminum. 

confirmed. 












Group III. 


81 


Experiment 25. 

Title: Analysis of an Unknown Solution which may 
contain any of the Metals of the HC1, H 2 S and NH 4 OH 
Groups. 

1. Separation into Groups. Follow the directions given 
in Introduction 4. 

2 . Analysis of the HC1 Group. Follow the directions 
given in Experiment 4 beginning with paragraph 2. 

3. Separation of the H 2 S Group into Parts I and II. 
Follow the directions given in Experiment 19 paragraph 3. 

4. Analysis of the H 2 S Group: Part I. Follow the direc¬ 
tions given in Experiment 11 beginning with paragraph 2. 

5. Analysis of the H 2 S Group: Part II. Follow the direc¬ 
tions given in Experiment 17 beginning with paragraph 2. 

6. Analysis of the NH 4 OH Group. Follow the directions 
given in Experiment 23 beginning with paragraph 2. 

7. The Written Record. Write all results of this experi¬ 
ment in tabular form. Follow the outlines given in Experi¬ 
ments 5,12,18 and 24. 


82 


Qualitative Analysis. 


GROUP IV. 

THE AMMONIUM SULPHIDE GROUP. 

This group contains the metals whose sulphides are in¬ 
soluble in water and alkaline solutions. Sulphuretted 
hydrogen gas might be used as the precipitating reagent, 
but for the scheme as given in this manual, ammonium 
sulphide is to be preferred. The metals in this group are: 


Cobalt.Co 

Nickel.Ni 

Manganese.Mn 

Zinc.Zn 


Ammonium chloride used when this group is precipitated 
with ammonium sulphide serves two purposes: (a) It holds 
any magnesium present in a mixture in solution as am¬ 
monium-magnesium chloride. (6) It prevents nickel from 
forming a brown colloidal solution with any excess of 
ammonium sulphide used in precipitating the group. To 
accomplish this second purpose a very strong solution of 
ammonium chloride must be used. 






Group IV. 


83 


Experiment 26 . 

Title: Tests for cobalt. Symbol Co. Valence 2. 

1. Cobalt Sulphide. Pour 5 c.c. of a solution of cobalt 
nitrate into a test-tube and add an equal volume of strong 
ammonium chloride solution: this will prevent the precipi¬ 
tation of the cobalt as a hydroxide in the next step. Make 
the mixture in the test-tube slightly alkaline with a few 
drops of dilute ammonium hydroxide and then add dilute 
yellow ammonium sulphide as long as a precipitate forms. 
This black precipitate is cobalt sulphide. The equation 
for its formation is: 

Co(N0 3 ) 2 + (NH 4 ) 2 S 2 -» CoS | + 2 NH4NO3 + s. 

Boil the contents of the test-tube gently for a minute and 
then filter them hot. Wash the precipitate three times 
with hot water on the filter paper. Reserve this washed 
precipitate for (2). 

2. Cobalt Sulphide is Insoluble in Cold Dilute HC1. By 

means of a stirring rod transfer a very small amount of the 
cobalt sulphide from (1) to a test-tube containing 5 c.c. of 
5 per cent hydrochloric acid. Shake the contents of the 
tube for a few moments. Does the cobalt sulphide dissolve? 

3. The Borax Bead Test. Seal a short piece of platinum 
wire into one end of a piece of glass tubing about three 
inches long. Make a loop an eighth of an inch in diameter 
in the free end of the wire. Clean this wire thoroughly by 
dipping it in a little dilute hydrochloric acid and holding 
it in the flame. Continue this treatment dipping and 
heating the wire until it no longer imparts any color to the 
Bunsen flame. Dip the loop while hot into a little borax. 
Again hold it in the flame. Continue in this manner until a 


84 


Qualitative Analysis. 


colorless glasslike bead is obtained. When borax is heated 
in this manner the following reaction occurs: 

Na 2 B 4 0 7 + A -> 2 NaB0 2 + B 2 0 3 . 

Touch this clear bead to the cobalt sulphide precipitate 
obtained in (1) and then again heat it in the Bunsen flame 
for about a minute. When the bead cools it will be a 
bright blue color. The reactions which occur are: 

CoS + 30 (from the air) -> CoO + S0 2 . 

2 NaB0 2 + B 2 0 3 + CoO -> 2 NaB0 2 .Co(B0 2 ) 2 

2 NaB0 2 .Co(B0 2 ) 2 , a double sodium cobalt metaborate, 
is the blue color. 

4. Cobalt Sulphide is Soluble in Hot Cone. HN0 3 . By 

means of a wash bottle transfer the cobalt sulphide pre¬ 
cipitate, obtained in (1) to an evaporating dish. Let the 
precipitate settle and then pour off as much of the water as 
possible. Add 5 c.c. of concentrated nitric acid to the 
cobalt sulphide and boil this mixture gently until the cobalt 
sulphide dissolves. Dilute the contents of the dish with 
5 c.c. of water and filter them into a beaker. To this clear 
filtrate add its own volume of strong ammonium chloride 
solution and then enough strong ammonium hydroxide to 
make the mixture moderately alkaline. Reserve for (5). 

5 . The Dimethylglyoxime Test. To the prepared solu¬ 
tion of cobalt nitrate from (4) add 5 drops of a one per cent 
alcoholic solution of dimethylglyoxime. A yellow brown 
color only will form. With nickel a very abundant pre¬ 
cipitate (rose red) is formed. The presence of cobalt does 
not interfere with this test. 

Conclusions, (a) (NH 4 ) 2 S 2 in the presence of an excess 
of NH 4 C1 and NH 4 OH precipitates CoS, black. 


Group IV. 


85 


(6) CoS is not soluble in cold dilute HC1. 

(c) CoS dissolves in hot concentrated nitric acid forming 
Co(N0 3 ) 2 . 

(d) Dimethylglyoxime in the presence of an excess of 
ammonium chloride and ammonium hydroxide forms a 
brown or yellow color with a solution of any cobalt com¬ 
pound. 

(e) Cobalt compounds color the borax bead bright blue 
due to the formation of 2 NaB0 2 .Co(B0 2 ) 2 . 


7 


86 


Qualitative Analysis. 


Experiment 27. 

Title: Tests for nickel. Symbol Ni. Valence 2. 

1. Nickel Sulphide. Pour 5 c.c. of a solution of nickel 
nitrate into a test-tube and add to it, its own volume of 
strong ammonium chloride solution (20 per cent). Now 
add dilute ammonium hydroxide until the mixture is 
slightly alkaline. To this mixture add dilute ammonium 
sulphide, a few drops at a time, until the precipitation of 
the nickel sulphide is complete. Boil the contents of the 
test-tube gently for two minutes and filter them hot. The 
chemical equation for the formation of the nickel sulphide is: 

Ni(N0 3 ) 2 + (NH 4 ) 2 S 2 -» NiS I + 2 NH 4 N0 3 + S. 

Wash the precipitate on the filter paper three times with 
hot water and then reserve it for (2). 

Note: The directions for the precipitation of the nickel 
sulphide, given above, should be followed exactly. If this 
is done the nickel sulphide will not form a colloidal solution 
(brown) with any excess of ammonium sulphide present. 
This colloidal solution if allowed to form gives trouble in 
the separation of this group. 

2. Nickel Sulphide is Insoluble in Cold Dilute HC1. 

Transfer a small quantity of the nickel sulphide to a test- 
tube by means of a stirring rod and add to it 5 c.c. of cold 
5 per cent hydrochloric acid. Shake the contents of the 
tube a few moments when it will be noted that nickel 
sulphide is not soluble in dilute hydrochloric acid. Reserve 
the balance of the black nickel sulphide on the filter paper 
for (3). 

3. The Borax Bead Test. Make a loop in one end of a 
piece of platinum wire about one eighth of an inch in 


Group IV. 


87 


diameter. Dip this loop into dilute hydrochloric acid and 
then heat it in the Bunsen flame until it imparts no color 
to the flame. While hot dip this wire into a little borax 
and again heat it until a clear colorless glasslike bead is 
obtained. Touch this to the nickel sulphide reserved 
form (2) and again heat it in the Bunsen flame. Use the 
oxidizing flame: the outer, nearly, invisible zone. Under 
these conditions nickel compounds form a brown colored 
bead. The chemical reactions are: 

Na 2 B 4 07 + A —> 2 NaB0 2 + B 2 03 . 

NiS + 30 (from the air) -» NiO + S0 2 . 

2 NaB0 2 + B 2 0 3 + NiO -> 2 NaB0 2 .Ni(B0 2 ) 2 (the brown 
color). Reserve the remaining nickel sulphide for (4). 

Note: This test for nickel fails if the reducing flame is 
used when heating the bead. In this case the bead is 
white and cloudy from the formation of metallic nickel. 
This test also fails in the presence of cobalt. If cobalt is 
present the blue cobalt bead will be formed. 

4. Nickel Sulphide is Soluble in Hot Concentrated HN0 3 . 
By means of a wash bottle transfer the nickel sulphide 
precipitate to an evaporating dish. Allow the precipitate 
to settle and then pour off as much of the water as possible. 
Add 5 c.c. of concentrated nitric acid to the nickel sulphide 
and boil this mixture gently until the nickel sulphide 
dissolves. Dilute the contents of the dish with 5 c.c. of 
water and filter them into a small beaker. Reserve this 
solution for (5). 

5. The Dimethylglyoxime Test. To the solution of 
nickel nitrate just prepared in (4) add its own volume of 
strong ammonium chloride solution and then enough con- 


88 


Qualitative Analysis. 


centrated ammonium hydroxide to make the mixture 
distinctly alkaline: avoid any great excess of the base. To 
this prepared solution of nickel add 5 drops of a one per 
cent solution of dimethylglyoxime in alcohol. The forma¬ 
tion of an abundant flocculent precipitate of a very char¬ 
acteristic pinkish red color indicates nickel. This test is 
very delicate showing very small amounts of nickel even 
when a considerable quantity of cobalt is present. The 
chemical equation for the reaction which takes place in 
this test is: 

Ni(N0 3 ) 2 + 2 [(CH,)C : N.OH] 2 

-> [(CH 3 )C : N.O] 4 NiH 2 + 2 HN0 3 . 

[(CH 3 )C : N.OH] 2 is the dimethylglyoxime. 

[(CH 3 )C : N.O] 4 NiH 2 is the red precipitate: an acid salt 
of nickel and the dimethylglyoxime. 

Conclusions, (a) (NH 4 ) 2 S 2 in the presence of an excess 
of NH 4 C1 and NH 4 OH precipitates NiS black. 

(6) NiS is not soluble in dilute (cold) HC1. 

(c) NiS dissolves in hot concentrated HN0 3 forming 
Ni(N0 3 ) 2 . 

(d) Nickel compounds color the borax bead brown when 
heated in the oxidizing flame. The bead is white and 
cloudy in the reducing flame. Cobalt interferes with this 
test. 

(e) Dimethylglyoxime in the presence of an excess of 
NH 4 C1 and NH 4 OH forms a pinkish red precipitate of* 
[(CH 3 )C : N.O] 4 NiH 2 . The presence of cobalt does not 
interfere with this test. 


Group IV. 


89 


Experiment 28 . 

Title: Tests for manganese. Symbol Mn. Valence 2 
and 6. 

A. 1 . Manganese Sulphide. Pour 5 c.c. of a solution of 
manganese nitrate into a test-tube and add an equal volume 
of strong ammonium chloride solution: this will prevent 
the precipitation of the manganese as a hydroxide in the 
next step. Now add dilute ammonium hydroxide a few 
drops at a time until the mixture smells strongly of ammonia. 
The addition now of a few drops of yellow ammonium 
sulphide produces a pinkish white precipitate of manganese 
sulphide. The chemical reaction is as follows: 

Mn(N0 3 ) 2 + (NH 4 ) 2 S 2 -> MnS 1 + 2 NH 4 N0 3 + S. 

Filter out this precipitate and wash it carefully. Reserve 
it for (2). 

2. Manganese Sulphide is Soluble in Dilute HC1. Pour 
10 c.c. of 5 per cent hydrochloric acid through the filter 
containing the manganese sulphide until the precipitate is 
completely dissolved. The acid should be used cold. The 
chemical reaction is: 

MnS + 2 HC1 -> MnCl 2 + H 2 S. 

Reserve this solution for (3). 

3. Manganese Hydroxide. To the solution reserved 
from (2) add potassium hydroxide solution a drop or two 
at a time until the mixture is just alkaline. This should 
be done slowly to avoid any heating of the mixture until 
the precipitate forms. The dirty white precipitate which 
forms is manganese hydroxide. The chemical reaction is: 

MnClj + 2 KOH -> Mn(OH) 2 1 + 2 KC1. 


90 


Qualitative Analysis. 


Now add an excess of the potassium hydroxide solution and 
bring the mixture to a boil. This is best done in a beaker, 
with constant stirring to avoid bumping. Manganese 
hydroxide is not soluble in an excess of potassium hydroxide 
solution. Filter this hot mixture and wash the precipitate 
on the filter paper. Set the precipitate aside on the filter 
paper and note how it darkens from exposure to the air. 
This is very characteristic. This dark color is due to the 
formation of Mn 3 0 4 and finally of Mn 2 0 3 . 

Note: Ammonium hydroxide produces the same pre¬ 
cipitate of manganese hydroxide as potassium hydroxide 
does. This precipitate, however, is not formed in the 
presence of an excess of ammonium chloride. Test these 
statements experimentally. 

B. 1 . Bead Tests for Manganese. The Borax Bead. 

Clean a piece of platinum wire upon the end of which a loop 
about an eighth of an inch in diameter has been formed 
by dipping it in a little dilute hydrochloric acid and then 
heating it in a Bunsen flame. Continue dipping and 
heating the wire until it imparts no color to the flame. 
Dip the hot loop of wire in borax and again hold it in the 
flame until a clear glass-like bead is formed. The reaction 
which takes place during this heating is: 

Na 2 B 4 0 7 -f- A —> 2 NaB0 2 -f- B 2 0 3 . 

Now dip this bead into any compound of manganese (the 
oxide from A, 3, above, may be used) and heat it a few 
moments in the oxidizing flame of the Bunsen burner. 
Upon cooling the bead will be a clear amethyst color. 

This amethyst color is due to the formation of a double 
borate of sodium and manganese. The chemical reaction is: 

2 Mn(OH) 2 + 0 (from the air) + A -> Mn 2 0 3 + 2 H 2 0. 
Mn 2 0 3 “b 3 Na 2 B 4 0 7 -j- A •—> 2[3 NaB0 2 .Mn(B0 2 ) 3 ]. 


Group IV. 


91 


Note: In this test care must be used to heat the bead in 
the oxidizing flame (outer zone) as the bead remains color¬ 
less in the reducing flame. 

2. The Sodium Carbonate Bead. Prepare a clean plat¬ 
inum wire with a loop on the end as in (1). Dip this in 
some sodium carbonate containing a little potassium 
chlorate, while hot. Hold this mixture in the Bunsen 
flame until it is melted into an opaque bead. Touch this 
bead to the manganese compound to be tested. Again 
heat the bead for a few moments in the outer Bunsen flame. 
The formation of a green opaque bead will result. The 
chemical reaction which takes place is as follows: 

3 Mn(OH) 2 + 2 KC10 3 + 3 Na 2 C0 3 + A 

-> 3 Na 2 Mn0 4 + 2 KC1 + 3 H 2 0 + 3 C0 2 . 

The green color is caused by the sodium manganate Na 2 - 
Mn0 4 . 

Conclusions, (a) (NH 4 ) 2 S 2 in the presence of an excess 
of NH 4 C1 and NH 4 OH precipitates MnS pinkish white. 

(b) MnS is soluble in dilute HC1 forming MnCl 2 . 

(c) KOH precipitates Mn(OH) 2 , dirty white, insoluble 
in excess. 

( 1 d ) Mn(OH) 2 darkens from exposure to the air due to 
the formation of Mn 3 0 4 and Mn 2 0 3 . 

(e) Manganese compounds color the borax bead amethyst 
and the sodium carbonate bead green. 


92 


Qualitative Analysis. 


Experiment 29. 

Title: Tests for zinc. Symbol Zn. Valence 2. 

1. Zinc Sulphide. Pour 5 c.c. of zinc nitrate solution 
into a test-tube and add an equal volume of strong am¬ 
monium chloride solution. This will prevent the pre¬ 
cipitation of the zinc as a hydroxide in the next step. 
Now add dilute ammonium hydroxide a few drops at a 
time until the mixture smells strongly of ammonia. The 
addition now of a few drops of ammonium sulphide pro¬ 
duces a white precipitate of zinc sulphide. The chemical 
reaction is as follows: • 

Zn(N0 3 ) 2 + (NH 4 ) 2 S 2 -> ZnS | + 2 NH 4 N0 3 + S. 

Filter out this precipitate and wash it carefully. Reserve 
it for (2). 

2. Zinc Sulphide is Soluble in Dilute HC1. Pour 10 c.c. 
of 5 per cent hydrochloric acid through the filter containing 
the zinc sulphide, reserved from (1), until this precipitate is 
completely dissolved. The acid should be used cold. The 
chemical reaction is: 

ZnS + 2 HC1 -> ZnCl 2 + H 2 S. 

Reserve this solution of zinc chloride for (3). 

3. Zinc Hydroxide. Hold a test-tube containing the zinc 
chloride solution under running cold water and while it is 
in this position add to it one drop of potassium hydroxide 
solution. This will produce a white precipitate of zinc 
hydroxide. Continue in this manner adding the potassium 
hydroxide a drop at a time, shaking the tube from time to 
time and keeping it cool under running cold water, until 


Group IV. 


93 


the precipitate first formed dissolves in the excess of potas¬ 
sium hydroxide. The reason for keeping the test-tube 
cool during this test is to avoid the formation of zinc oxide 
instead of the hydroxide which would occur if the solution 
became hot. This heating might happen from the addition 
of the potassium hydroxide to the mixture. Strong potas¬ 
sium hydroxide solution when added to water produces 
considerable heat just as strong acid does. As zinc oxide 
is not soluble in an excess of potassium hydroxide it might, 
if allowed to form, be mistaken for manganese, in an 
analysis. The chemical reaction for the solution of zinc 
hydroxide in potassium hydroxide is as follows: 

Zn(OH ) 2 + 2 KOH -> K 2 Zn0 2 + 2 H 2 0. 

K 2 Zn0 2 is potassium zincate. 

To this solution of zinc hydroxide in excess of potassium 
hydroxide now add a few drops of ammonium sulphide or 
pass sulphuretted hydrogen gas through it for a moment. 
In either case a white precipitate of zinc sulphide will form. 

Note: Ammonium hydroxide produces the same pre¬ 
cipitate of zinc hydroxide as potassium hydroxide does, 
soluble in excess of the ammonium hydroxide. This pre¬ 
cipitate is not formed in the presence of ammonium chloride. 
Test these statements. 

Conclusions, (a) (NH 4 ) 2 S 2 in the presence of an excess 
of NH 4 C1 and NH 4 OH precipitates ZnS, white. 

( b ) ZnS is soluble in dilute HC1 forming ZnCl 2 . 

(c) KOH precipitates Zn(OH) 2 , white, soluble in excess. 

( d ) ZnS is re-precipitated from (c) by (NH 4 ) 2 S 2 or H 2 S. 


94 


Qualitative Analysis. 


Experiment 30. 

Title: Separation of the Metals of the Ammonium 
Sulphide Group. This solution is known to contain Co, Ni, 
Mn, and Zn ions. 

1 . Precipitation of the Group. Pour 5 c.c. of the solution 
containing the group into a beaker. Add 25 c.c. of a strong 
solution of ammonium chloride (20 per cent) and make the 
mixture alkaline with a few drops of dilute ammonium 
hydroxide. Test with litmus paper. Avoid any great 
excess of base. Now add 10 c.c. of yellow ammonium 
sulphide solution and then bring the mixture to a boil and 
continue boiling gently for 2 minutes. Filter at once. 
This precipitate contains the sulphides of cobalt, nickel, 
manganese and zinc. Wash it three times with hot water 
and reserve it for (2). If the above directions are followed 
exactly the group will be completely precipitated and the 
nickel will not run through the filter as brown colloidal 
nickel sulphide. The filtrate should be distinctly yellow 
from the excess of ammonium sulphide. If it is discard it. 
If not add more ammonium sulphide to insure the complete 
precipitation of the group. If more precipitate forms add 
it to that on the filter paper. 

2. The Separation of Cobalt and Nickel Form Manganese 
and Zinc. Place the filter paper containing the precipitate, 
reserved from ( 1 ) in an evaporating dish. Add 10 c.c. of a 
5 per cent solution of cold hydrochloric acid. Stir the 
mixture until the precipitate is all removed from the filter 
paper. Discard this paper. Continue stirring the mixture 
for half a minute and then filter it cold. Reserve the 
clear filtrate, which contains the manganese and zinc as 
chlorides, for (5). Wash the residue on the filter paper 
twice with hot water and reserve it for (3). 


Group IV. 


95 


3. The Test for Cobalt. Make a loop an eighth of an 
inch in diameter in the end of a platinum wire. Clean this 
thoroughly by dipping it in dilute hydrochloric acid and 
then heating it until it imparts no color to the Bunsen 
flame. Dip the hot wire into a little borax and again heat 
in the Bunsen flame until a colorless glassy bead is formed. 
It must be colorless. Touch this bead to the precipitate 
reserved from (2) and again heat it strongly for a half a 
minute in the flame. A bright blue clear bead indicates 
cobalt. If cobalt is absent in an unknown mixture nickel 
will color this bead brown if the oxidizing flame is used. 

4. The Test for Nickel. Puncture the filter paper con¬ 
taining the nickel and cobalt sulphides and wash these into a 
beaker with the wash bottle. Allow the precipitate to 
settle and pour off as much of the water as possible. Pour 5 
c.c. of concentrated nitric acid on the precipitate. Boil this 
mixture gently until the precipitate is dissolved. Dilute 
the solution thus produced with 5 c.c. of water. Filter it 
if it is not perfectly clear. To the clear solution add its 
own volume of ammonium chloride solution and then 
enough strong ammonium hydroxide to make the mixture 
moderately alkaline. Test with litmus paper. To this 
alkaline solution add 5 drops of a 1 per cent alcoholic solu¬ 
tion of dimethylglyoxime. The formation of an abundant 
flocculent precipitate of a characteristic pink red color 
indicates nickel. In the absence of nickel, cobalt produces 
a yellow color only. 

5. The Test for Manganese. To the hydrochloric acid 
filtrate set aside in (2) add potassium hydroxide solution 
in excess. The beaker must be kept cool during this 
process. Do this by running cold water on the outside of 
the beaker and adding the base very slowly. Test with 
litmus paper for a strong excess of the potassium hydroxide. 


96 


Qualitative Analysis. 


Now boil the mixture. The precipitate which has formed 
is manganese hydroxide and indicates manganese. Filter 
out this precipitate at once and wash it with hot water. 
Reserve the filtrate for (6). If the precipitate on the filter 
paper darkens rapidly upon standing due to the formation 
of an oxide of manganese, the presence of manganese is 
confirmed. To further confirm manganese: make a bead 
of a mixture of sodium carbonate and potassium chlorate. 
This will be white and opaque. Touch this to the pre¬ 
cipitate of manganese on the filter paper and again heat it 
strongly in a Bunsen flame. The formation of a green 
color due to the formation of sodium manganate confirms 
manganese. 

6 . The Test for Zinc. Pass sulphuretted hydrogen gas 
through the filtrate reserved from (5) for a few moments. 
The formation of a white precipitate of zinc sulphide indi¬ 
cates the presence of zinc. Filter and wash this precipitate. 
Tear off a piece of the filter paper which is well covered 
with the zinc sulphide. Pour 3 drops of a solution of 
cobalt nitrate on the zinc sulphide and then holding the 
wet paper in a tongs or tweezers heat it in a Bunsen flame 
until the water evaporates and the paper is burned. On 
the ash that remains there will be a bright green color due 
to the formation of cobalt zincate, CoZn02, Rinmanns 
green. The formation of this color confirms the presence of 
zinc. 

Conclusions. For further details of the individual 
tests the student is referred to Experiments 26-29. The 
written record of this experiment should include details 
of every operation and test, as well as chemical equations 
for all reactions involved. 


Group IV. 


97 


Experiment 31. 

Title: The analysis of an unknown solution which may 
contain any or all of the metals of the ammonium sulphide 
group. 

1. Directions. Proceed exactly as in the previous experi¬ 
ment, No. 30. 

2. The Written Record. Having written out the separa¬ 
tion for this group in detail in the last experiment, No. 30, 
a shorter method may be used for the results of this experi¬ 
ment and any others which include this group. The 
following tabular record is suggested. 


Qualitative Analysis 


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DO 

© 

Si 

D 3 Ch 

m © 

C(3 a 




© o 


© 

> 

Si 

© 

m 

© 

PS 


S3 

<3 

Si 

o 

























Group IV. 


99 


Experiment 32. 

Title: An Analysis of an Unknown Solution which may 
contain any of the Metals of Groups I-IV. 

1. Separation into Groups. Follow the directions given 
in Introduction 4. 

2. Analysis of the HC1 Group. Follow the directions 
given in Experiment 4 beginning with paragraph 2. 

3. Separation of the H 2 S Group into Parts I and II. 
Follow the directions given in Experiment 19 paragraph 3. 

4. Analysis of the H 2 S Group: Part I. Follow the direc¬ 
tions given in Experiment 11 beginning with paragraph 2. 

5. Analysis of the H 2 S Group: Part II. Follow the direc¬ 
tions given in Experiment 17 beginning with paragraph 2. 

6 . Analysis of the NH 4 OH Group. Follow the directions 
given in Experiment 23 beginning with paragraph 2. 

7. Analysis of the (NH 4 ) 2 S 2 Group. Follow the direc¬ 
tions given in Experiment 30 beginning with paragraph 2. 

8 . The Written Record. Write all results of this experi¬ 
ment in tabular form. Follow the outlines given in Experi¬ 
ments 5, 12, 18, 24 and 31. 


100 


Qualitative Analysis. 


GROUP V. 

THE AMMONIUM CARBONATE GROUP. 

This group contains the metals whose carbonates are 
insoluble in alkaline solutions. The solution is made alka¬ 
line with ammonium hydroxide and then precipitated with a 
strong solution of ammonium carbonate. The metals in 
this group are: 


Barium.Ba 

Strontium.Sr 

Calcium.Ca 





Group V. 


101 


Experiment 33. 

Title : Tests for barium. Symbol Ba. Valence 2. 

1. Barium Carbonate. Pour 5 c.c. of a solution of 
barium nitrate into a test-tube and add just enough dilute 
ammonium hydroxide to make the mixture slightly alkaline. 
Now add ammonium carbonate solution a few drops at a 
time as long as the precipitate of barium carbonate forms. 
The chemical equation for the formation of this precipitate 
is as follows: 

Ba(N0 3 ) 2 + (NH 4 ) 2 C0 3 -> 1 BaC0 3 + 2 NH 4 N0 3 . 

The ammonium hydroxide plays no part in the formation 
of the barium carbonate precipitate but is present only to 
neutralize any small amount of acid which might be present. 
All the carbonates of this group are soluble in a number of 
very dilute acids: viz. HC1. 

Filter and wash this precipitate of barium carbonate and 
reserve it for (2). 

2. Barium Carbonate is Soluble in Dilute HC1. Pour 
5 c.c. of dilute hydrochloric acid through the precipitate on 
the filter paper. Note the effervescence of carbon dioxide 
gas as the precipitate dissolves in the acid. The equation 
for this solution is: 

BaC0 3 + 2 HC1 -> BaCl 2 + H 2 0 + C0 2 . 

If the barium carbonate has not completely dissolved in 
the acid pour this acid through the filter until the solution 
of the precipitate its complete. Place this clear solution 
in an evaporating dish and boil it down to dryness. This 
must he done carefully with a very low flame toward the qnd,, 
8 


102 


Qualitative Analysis. 


Over-heating the barium chloride would change it to barium 
oxide. This change must be avoided if the next step is to be 
successful Reserve this dry barium chloride for ( 3 ). 

3. Barium Chloride is Insoluble in Ethyl Alcohol. Treat 
the solid barium chloride, after it has cooled, with 10 c.c. 
of 95 per cent ethyl alcohol. Stir the contents of the 
evaporating dish for some time with this alcohol. Filter 
the contents of the dish through a filter paper moistened 
with alcohol: not water. Add a few drops of dilute sulphuric 
acid to the alcohol filtrate. No precipitate will form 
proving that the barium chloride did not dissolve in the 
alcohol. Barium sulphate is a very insoluble substance. 
Reserve the barium chloride on the filter paper for ( 4 ). 

4. Barium Chloride is Soluble in Water. Pour 10 c.c. of 
cold water through the filter paper reserved from ( 3 ). 
Repeat the pouring until all the barium chloride is dissolved. 
Reserve this solution for ( 5 ). 

5. A Flame Test for Barium. Clean a mounted platinum 
wire by dipping it in dilute hydrochloric acid and holding 
it in a Bunsen flame until it imparts no color to the flame. 
Dip this cleaned wire into the barium chloride solution 
reserved from (4) and then hold it in the Bunsen flame. 
A yellowish-green color, very characteristic of barium, will 
be imparted to the flame. Reserve the balance of the 
barium chloride solution for ( 6 ). 

6 . Barium Sulphate is Insoluble in Water or HC1. 
Add a few drops of dilute sulphuric acid to the solution 
reserved from (5). A heavy white precipitate of barium 
sulphate forms. This precipitate is formed through the 
following chemical reaction: 


BaCl 2 + H 2 S0 4 -> | BaS0 4 + 2 HC 1 . 


Group V. 


103 


Barium sulphate is insoluble in water solutions of prac¬ 
tically all chemical reagents. It is also insoluble in strong 
hydrochloric acid. Add a large excess of HC1 (cone.) to 
the test-tube containing the precipitate to test this point. 

Conclusions, (a) (NH 4 )2C0 3 precipitates BaC0 3 from 
neutral and alkaline solutions. 

(b) BaC0 3 is readily soluble in dilute HC1, forming BaCl 2 . 

(c) BaCl 2 is insoluble in ethyl alcohol, C 2 H 5 OH. 

(d) BaCl 2 is readily soluble in cold water. 

(e) Barium compounds impart a yellowish-green color 
to the Bunsen flame. 

(/) Dilute H 2 S0 4 precipitates very insoluble BaS0 4 . 
BaS0 4 is insoluble in concentrated HC1. 


104 


Qualitative Analysis. 


Experiment 34. 

Title: Tests for strontium. Symbol Sr. Valence 2. 

1. Strontium Carbonate. Pour 5 c.c. of strontium ni¬ 
trate solution into a test-tube and add just enough dilute 
ammonium hydroxide to make the mixture slightly alkaline. 
Now add ammonium carbonate solution a few drops at a 
time as long as a precipitate of strontium carbonate forms. 
The chemical equation for this reaction is: 

Sr(N0 3 ) 2 + (NH 4 ) 2 C0 3 -» 1 SrC0 3 + 2 NH 4 N0 3 . 

As in the case of barium the presence of the ammonium 
hydroxide neutralizes any acid which might be present 
which would cause the solution of the strontium carbonate. 
There is also a tendency for ammonium carbonate solution 
to lose ammonia and change to ammonium bi-carbonate 
solution. Thus: 

(NH 4 ) 2 C0 3 -> HNH 4 C0 3 + NH 3 . 

When ammonium bi-carbonate solution acts upon stron¬ 
tium solutions or solutions of the other metals of this 
group carbon dioxide is liberated thus: 

Sr(N0 3 ) 2 + 2 HNH 4 C0 3 -> | SrC0 3 

+ 2 NH 4 N0 3 + H 2 0 + C0 2 . 

The carbonic acid produced by the solution of carbon 
dioxide gas in water has a tendency to dissolve the carbon¬ 
ates of the metals of this group especially barium carbonate. 
The presence of the ammonium hydroxide prevents this and 
causes the complete precipitation of the metals of this 


Group V* 


105 


group for ammonium hydroxide reacts with ammonium 
bi-carbonate forming the normal carbonate. Thus: 

HNH 4 CO 3 + NH 4 OH -> (NH 4 ) 2 C0 3 + H 2 0. 

Filter out the precipitate of strontium carbonate and wash 
it. Reserve this washed precipitate for (2). 

2. Strontium Carbonate is Soluble in Dilute HC1. Pour 
5 c.c. of dilute hydrochloric acid through the filter con¬ 
taining the strontium carbonate. Note the effervescence 
of carbon dioxide as the white residue on the filter paper 
dissolves. The reaction for this change is shown in the 
following equation: 

SrC0 3 + 2 HC1 -» SrCl 2 + H 2 0 + C0 2 . 

Evaporate the strontium chloride solution carefully to 
dryness. Do not over heat or the chloride will be changed 
to oxide. Reserve this dry strontium chloride for (3) 
and (4). 

3. A Flame Test for Strontium. Clean a mounted plat¬ 
inum wire by dipping it in dilute hydrochloric acid and 
heating it in a Bunsen flame until it imparts no color to the 
flame. Dissolve a few milligrams of the strontium chloride 
in a few drops of water. Dip the cleaned platinum wire 
into this solution and heat it in the Bunsen flame. Stron¬ 
tium compounds impart a carmine-red color to the Bunsen 
flame. This color burns away quickly. 

4. Strontium Chloride is Soluble in Ethyl Alcohol. To 
the balance of the cool dry strontium chloride in the evapor¬ 
ating dish add 10 c.c. of ethyl alcohol. Stir this mixture 
with a glass rod until the solid is all dissolved. If this 
alcohol solution is not clear filter it. Reserve this clear 
solution of strontium chloride in alcohol for (5). 


106 


Qualitative Analysis. 


5. Strontium Sulphate is Insoluble in Alcohol. To the 

clear solution reserved from (4) add dilute sulphuric acid a 
few drops at a time as long as the precipitate of strontium 
sulphate forms. The equation for this reaction is: 

SrCl 2 + H 2 S0 4 -> 1 SrS0 4 + 2 HC1. 

Filter off this precipitate and wash it. Reserve it for (6). 

6. Strontium Sulphate is Insoluble in (NH 4 ) 2 S0 4 and 
NH 4 OH. Puncture the filter paper and wash the strontium 
sulphate reserved from (5) into a beaker with 10 c.c. of a 
mixture of equal parts of a strong solution of ammonium 
sulphate and dilute ammonium hydroxide. Boil the con¬ 
tents of the beaker for a minute slowly. Strontium sulphate 
will not dissolve in this reagent. This test distinguishes it 
from calcium sulphate which readily dissolves in boiling 
ammonium sulphate made alkaline with ammonium 
hydroxide. 

Conclusions, (a) (NH 4 ) 2 C0 3 precipitates SrC0 3 from 
neutral and alkaline solutions. 

(b) SrC0 3 is soluble in dilute HC1, forming SrCl 2 . 

(c) Strontium compounds impart a carmine-red color to 
the Bunsen flame. 

(d) SrCl 2 is readily soluble in ethyl alcohol, C 2 H 5 OH. 

(e) Dilute H 2 S0 4 precipitates SrS0 4 from the above 
solution of SrCl 2 in C 2 H 5 OH. 

(/) SrS0 4 is not soluble in boiling (NH 4 ) 2 S0 4 and 
NH 4 OH. Distinction from Calcium. 


Group V. 


107 


Experiment 35. 

Title: Tests for calcium. Symbol Ca. Valence 2. 

1. Calcium Carbonate. Pour 5 c.c. of calcium nitrate 
solution into a test-tube and make it slightly alkaline with 
dilute ammonium hydroxide. To this mixture add a solu¬ 
tion of ammonium carbonate a few drops at a time as long 
as a precipitate of calcium carbonate forms. The chemical 
equation for this reaction is 

Ca(N0 3 ) 2 + (NH 4 ) 2 C0 3 -» | CaC0 3 + 2 NH 4 N0 3 . 

Filter and wash this precipitate and reserve it for (2). 

2. Calcium Carbonate is Soluble in Dilute HC1. Pour 
5 c.c. of dilute hydrochloric acid through the filter paper 
containing the calcium carbonate until this substance is 
all dissolved. The chemical equation for this solution is: 

CaC0 3 + 2 HC1 -> CaCl 2 + C0 2 + H 2 0. 

Reserve this clear solution for (3). 

3. A Flame Test for Calcium. Clean a mounted plat¬ 
inum wire by dipping it in dilute hydrochloric acid and 
heating it in the Bunsen flame until the wire imparts no 
color to the flame. Dip this wire in the solution reserved 
from (2) and again heat the wire in the Bunsen flame. 
Calcium compounds impart a reddish-yellow color to the 
Bunsen flame. Reserve the balance of the solution of 
calcium chloride for (4). 

4. Calcium Chloride is Soluble in Ethyl Alcohol. Care¬ 
fully evaporate the solution reserved from (3) to dryness. 
Avoid over-heating. Use a low flame as the liquid boils away. 
When the evaporating dish has cooled add 10 c.c. of alcohol 


108 


Qualitative Analysis. 


to its contents and stir the mixture until the calcium 
chloride is dissolved. If the solution is not entirely clear 
filter it and reserve the clear solution for (5). 

5. Calcium Sulphate is Insoluble in Ethyl Alcohol. To 
the alcohol solution reserved from (4) add dilute sulphuric 
acid a few drops at a time as long as a precipitate of calcium 
sulphate forms. The equation for this reaction is: 

CaCl 2 + H 2 S0 4 -»| CaS0 4 + 2 HC1. 

Filter and wash this precipitate on the filter paper. Re¬ 
serve the washed precipitate for (6). 

6. Calcium Sulphate is Soluble in Hot Alkaline (NH 4 ) 2 - 
S0 4 . Puncture the filter paper reserved from (5) and wash 
the precipitate of calcium sulphate into a beaker with 10 
c.c. of a mixture of equal parts of a strong solution of 
ammonium sulphate and dilute ammonium hydroxide. 
Bring the contents of the beaker to a boil and continue to 
boil slowly until the calcium sulphate is completely dis¬ 
solved. If the solution is not perfectly clear filter it. Re¬ 
serve the clear solution of calcium sulphate for (7). 

7. Ammonium Oxalate Precipitates Calcium Oxalate. 
To the solution just reserved from (6) add about 5 c.c. of a 
solution of ammonium oxalate. If a fine white precipitate 
of calcium oxalate does not form at once, warm the mixture 
(do not boil) and set it aside for a few moments. This 
reaction is very characteristic of calcium. The chemical 
equation is as follows: 

CaS0 4 + (NH 4 ) 2 C 2 0 4 -> | CaC 2 0 4 + (NH 4 ) 2 S0 4 . 

Conclusions, (a) (NH 4 ) 2 C0 3 precipitates CaC0 3 from 
neutral and alkaline solutions of calcium compounds. 

(b) CaC0 3 is soluble in dilute HC1 forming CaCl 2 . 


Group V. 


109 


(c) Calcium compounds impart a brick-red or reddish- 
yellow color to the Bunsen flame. 

( d ) CaCl 2 is soluble in C 2 H 5 OH. 

(e) Dilute H 2 S0 4 precipitates CaS0 4 even from dilute 
calcium solutions in the presence of ethyl alcohol, C 2 H 5 OH. 

(/) CaS0 4 is soluble in hot (NH 4 ) 2 S0 4 if it is made alka¬ 
line with NH 4 OH. 

( g ) (NH 4 ) 2 C 2 0 4 precipitates CaC 2 0 4 . CaC 2 0 4 is readily 
soluble in HC1 and HN0 3 , but insoluble in oxalic or acetic 
acids. 


110 


Qualitative Analysis. 


Experiment 36. 

Title: Separation of the metals of the Ammonium 
Carbonate Group. This solution is known to contain Ba, 
Sr, and Ca ions. 

1. Precipitation of the Group. Pour 5 c.c. of the solution 
containing the group into a test-tube. If there is any 
possibility of the Sixth Group being present add 5 c.c. of 
strong ammonium chloride solution to the contents of the 
test-tube. This ammonium chloride is added to prevent 
any magnesium ion present from precipitating out as a 
hydroxide in the next step. If magnesium is known to be 
absent omit the ammonium chloride. Now add enough 
dilute ammonium hydroxide to the contents of the test- 
tube to make the mixture distinctly alkaline. Next add 
ammonium carbonate solution a few drops at a time as 
long as a precipitate forms. Bring the mixture to a boil, 
if ammonium chloride has not been added, otherwise simply 
warm the mixture and filter it at once. Barium carbonate 
is soluble in boiling ammonium chloride solution: hence the 
precaution just noted. The precipitate on the filter paper 
contains barium, strontium and calcium carbonates. The 
equation for the formation of this precipitate is given under 
the tests for these metals. Wash the precipitate on the 
filter paper and reserve it for (2). 

2. Tests for Barium. Pour 5 c.c. of dilute hydrochloric 
acid through the filter paper reserved form (1) until the 
precipitate on the filter paper is all dissolved. Put this 
solution into an evaporating dish and slowly boil of the 
liquid until nothing remains but the dry chlorides of the 
metals of this group. Care must be taken not to overheat 
these chlorides or they will be changed to oxides. This would 
seriously interfere with the next step. When the evapor- 


Group V. 


Ill 


ating dish is cool treat the residue it contains with 10 c.c. 
of ethyl alcohol. Stir this mixture thoroughly for a minute 
grinding the solids in the alcohol with a small pestle. A 
stirring rod will do but the intimate mixture of the alcohol 
with all parts of the solids will be slower. Allow the un¬ 
dissolved residue to settle and then pour the liquid only 
upon a filter moistened with alcohol, not water. Treat the 
residue in the dish with 5 c.c. of alcohol in the same manner 
as before but this time pour the entire contents of the dish 
into the same filter and add the clear alcohol filtrate to the 
first alcohol filtrate. Wash the residue on the filter paper 
with 5 c.c. of fresh alcohol and also add this wash liquid 
to the mixed filtrates. Set this alcohol filtrate aside for 
(3) and (4). The residue on the filter paper is barium 
chloride which is not soluble in alcohol. Pour 5 c.c. of 
water through the filter paper until the barium chloride is 
entirely dissolved. Clean a mounted platinum wire 
thoroughly until it imparts no color to the Bunsen flame. 
Dip this wire in the water solution just made and again 
hold it in the Bunsen flame. The production of a yellowish- 
green color in the Bunsen flame indicates barium. To the 
balance of the solution of barium chloride add dilute sul¬ 
phuric acid a few drops at a time as long as a precipitate 
forms. The formation of a heavy white precipitate of 
barium sulphate insoluble in strong hydrochloric acid, 
confirms the presence of barium. 

3. Tests for Strontium. To the alcohol filtrate reserved 
from (1) add dilute sulphuric acid a little at a time as long 
as a precipitate forms. When precipitation is complete 
filter off the precipitate and discard the filtrate. The 
filter paper now contains strontium and calcium sulphates. 
Puncture this filter paper and wash these sulphates through 
into a beaker with 10 c.c. of a mixture of equal parts of 


112 Qualitative Analysis. 

strong ammonium sulphate solution and dilute ammonium 
hydroxide. Boil this mixture slowly for 3 minutes and 
then filter the solution hot. The calcium sulphate will 
have dissolved in the hot ammonium sulphate. Reserve 
this filtrate for (4). Strontium sulphate is not soluble in 
the reagent just used: it remains on the filter paper. Wash 
this precipitate with water. Test a little of this washed 
precipitate by dipping a clean platinum wire into it and 
holding the wire in the Bunsen flame. If the flame is 
colored a carmine-red which burns away quickly the 
presence of strontium is shown. If there is any doubt about 
this test the strontium sulphate may be dissolved in strong 
hot hydrochloric acid and the flame test again made. The 
hydrochloric acid will increase the delicacy of this flame test. 

4. Tests for Calcium. To the solution of calcium sul¬ 
phate in ammonium sulphate reserved from (3) add 5 c.c. 
of ammonium oxalate solution and warm. The formation 
of a white precipitate of calcium oxalate indicates calcium. 
When the calcium is present in very small amount this 
precipitate forms slowly after standing for some minutes. 
Add strong hydrochloric acid to the test-tube containing 
this precipitate of calcium oxalate until the precipitate, 
after shaking, is completely dissolved. Boil this solution 
down in an evaporating dish until only a small amount 
remains. Test this on a clean mounted platinum wire in 
the Bunsen flame. If the flame is colored a reddish- 
yellow, the presence of calcium is confirmed. 

Conclusions, (a) Barium is separated from the other 
members of this group because its chloride will not dissolve 
in alcohol. Strontium and calcium chlorides are soluble 
in alcohol. Water dissolves barium chloride and sulphuric 
acid precipitates barium sulphate. Barium compounds 
color the Bunsen flame a yellowish green. 


Group V. 


113 


(b) Strontium is separated from the other members of 
this group because its chloride dissolves in alcohol; because 
its sulphate is insoluble in alcohol and alkaline ammonium 
sulphate. Strontium compounds color the Bunsen flame a 
carmine-red. 

(c) Calcium is separated from the other members of'this 
group because its chloride is soluble in alcohol; because its 
sulphate dissolves in hot alkaline ammonium sulphate 
solution. From this solution ammonium oxalate precipi¬ 
tates it as calcium oxalate. Calcium compounds color the 
Bunsen flame a reddish-yellow. 


114 


Qualitative Analysis. 


Experiment 37 . 



Title: Analysis of an Unknown Solution which may con¬ 
tain Ba, Sr and Ca ions only. 

1. Procedure. Follow the method of analysis given in 
the preceding experiment exactly. 

2. The Written Record. Having analyzed a known solu¬ 
tion in this group and having written up the record of this 
separation in detail, the following brief tabular form of 
record may be used for the results of this analysis and for 
all subsequent analyses in which this group occurs. 


Result: Analysis of the (NH 4 ) 2 C0 3 Group. 


The Group. 

Barium (1). 

Strontium (2). 

Calcium (3). 

5 c.c. solution 

Residue 1 

Filtrate 2 

Filtrate 4 

+ 

+ 

+ 

-f* 

(NH 4 C1) 

H 2 0. 

H 2 S0 4 (excess). 

(NH 4 ) 2 C 2 0 4 

NH 40 H 

Part 1. 

Filter, discard 

warm. 

(NH 4 ) 2 C0 3 . 

Make flame test. 

filtrate. 

White ppt. is 

Filter and wash. 

Greenish-yellow 

Ppt. 

CaC 2 0 4 . 

Dissolve ppt. in 

color. 

+ 

Indicates 

HC1. 

Indicates barium. 

NH 4 OH and 

calcium. 

Evaporate to 

Part 2. 

(NH 4 ) 2 S0 4 

+ 

dryness. 


+ 

cone. HC1 to 

Treat with 

+ 

Boiling. 

solution. 

C 2 H 5 OH. 

Dilute H 2 S0 4 . 

Filter. 

Boil to 2 c.c. 

Filter. 

White ppt. is 

Reserve filtrate 

Flame test 

Reserve residue 1 

BaS0 4 . 

4 for (3). 

gives yellow- 

for (1). 

Confirms 

Make flame test 

red color, con¬ 

Reserve filtrate 2 
for (2) (3). 

barium. 

on washed ppt. 
Carmine-red 
flame. 

Indicates 

strontium. 

firms calcium. 











Group V. 


115 


Experiment 38. 

Title: Analysis of an Unknown Solution which may con¬ 
tain any of the metals of Groups I-V. 

1. Separation of the Metals into Groups. Follow the 
directions given in Introduction 4. 

2. Analysis of the HC1 Group. Follow the directions 
given in Experiment 4, beginning with paragraph 2. 

3. Separation of the H 2 S Group into Parts I and II. 
Follow the directions given in Experiment 19, paragraph 3. 

4. Analysis of the H 2 S Group: Part I. Follow the direc¬ 
tions given in Experiment 11, beginning with paragraph 2. 

5. Analysis of the H 2 S Group: Part II. Follow 1/he direc¬ 
tions given in Experiment 17, beginning with paragraph 2. 

6. Analysis of the NH 4 OH Group. Follow the directions 
given in Experiment 23, beginning with paragraph 2. 

7. Analysis of the (NH 4 ) 2 S 2 Group. Follow the direc¬ 
tions given in Experiment 30, beginning with paragraph 2. 

8. Analysis of the (NH 4 ) 2 C0 3 Group. Follow the direc¬ 
tions given in Experiment 36, beginning with paragraph 2. 

9. The Written Record. Write all results of this experi¬ 
ment in tabular form. Follow the outlines given in Experi¬ 
ments 5, 12, 18, 24, 31 and 37. 


Qualitative Analysis. 


116 


GROUP VI. 

THE ALKALI GROUP. 

This group contains the metals whose chlorides, sulphides, 
hydroxides and carbonates are all soluble in the reagents 
used to effect the precipitation of the other groups: hence 
they are found in the final filtrate remaining after the first 
five groups have been removed. The metals in this group 


are: 

Magnesium.Mg 

Ammonium.NH 4 

Sodium (Natrium).Na 

Potassium (Kalium).K 


The ammonium radical is of course not an actual metal. 
But since this radical is capable of forming compounds in 
which it plays the part of a metal it may be so considered. 






Group VI. 


117 


Experiment 39. 

Title: Tests for the metals of the “Sixth Group.” This 
solution is known to contain Mg, Na, K, and NH 4 ions. 

1. Tests for the Ammonium Radical—NH 4 . To 5 c.c. of 
the solution containing this group add an excess of sodium 
hydroxide solution and warm the mixture. The odor of 
ammonia gas indicates the ammonium radical —NH 4 . If 
this radical is present in very small amount its odor might 
not be detected. In this case hold a small piece of wet red 
litmus paper in the mouth of the test-tube in which the 
mixture is being heated. Do not allow the litmus paper to 
touch the sides of the tube. If the ammonium radical is 
present, even in very small amount, the red litmus will turn 
blue. Ammonia is the only base which is volatile: hence 
if the paper is allowed to come in contact with the evolved 
gases only it indicates the presence of the ammonium radical 
if it turns blue. 

If any of the Groups 2-5 have also been present in the 
mixture then ammonium compounds have been added to it 
in the analysis of these groups and in such case the test for 
the ammonium radical must be made upon some of the 
original solution. 

2. The Test for Magnesium. Pour 5 c.c. of the solution 
of the “Sixth Group” into a test-tube and add to it its own 
volume of ammonium chloride solution. Now make the 
mixture strongly alkaline with dilute ammonium hydroxide. 
If any of the groups 2-5 have been present and the solution 
under analysis is the filtrate from which these groups have 
been removed, then the two steps just taken are unneces¬ 
sary as the solution will then contain both ammonium 
chloride and ammonium hydroxide added in the separation 
of these groups. Next add an excess of di-sodium acid 

9 


118 


Qualitative Analysis. 


phosphate solution. This will produce a white crystalline 
precipitate of magnesium-ammonium phosphate and indi¬ 
cates the presence of magnesium. Filter out this precipitate 
and reserve the filtrate for (4). If the precipitate is light 
and flocculent it is probably aluminum phosphate and 
should not be mistaken for magnesium in an unknown 
solution. If this light precipitate forms proceed as follows. 
Wash the precipitate on the filter paper and then puncture 
the filter paper and wash the precipitate into a test-tube 
with 10 c.c. of sodium hydroxide solution. Warm and 
shake well. If the white precipitate is aluminum phosphate 
it will be completely dissolved. Magnesium-ammonium 
phosphate is not soluble in this reagent and will remain 
undissolved. Such an insoluble residue confirms the pres¬ 
ence of magnesium. 

3. The Test for Sodium. Dip a thoroughly cleaned plat¬ 
inum wire, which imparts no color to the Bunsen flame, 
into a fresh portion of the solution containing the “Sixth 
Group.” Heat this in the Bunsen flame. If a charac¬ 
teristic yellow color is imparted to the flame the presence 
of sodium is shown. No precipitate tests for sodium are 
usually used since it forms very few insoluble compounds. 

4. Tests for Potassium. Dip a thoroughly cleaned plat¬ 
inum wire, which imparts no color to the Bunsen flame, into 
the filtrate reserved from (2). Heat this in the Bunsen 
flame and view the flame produced through a piece of blue 
glass. A red-violet or lilac colored flame seen through the 
blue glass indicates potassium. 

If there is any doubt about the test for potassium just 
given evaporate this filtrate reserved from (2) containing 
the potassium ion to dryness in an evaporating dish and 
continue the heating after the water is driven off until no 
more white fumes (ammonium compounds) appear. When 


Group VI. 


119 


the dish cools treat the residue with 5 c.c. of water and 
after thorough stirring filter to obtain a clear solution. 
Put a few drops of this into a watch glass and add a drop 
or two of a solution of platinic chloride. The formation of a 
yellow precipitate of potassium chloro-platinate which 
remains upon stirring confirms the presence of potassium. 

Conclusions, (a) The ammonium radical must be 
tested for in the original solution in mixtures where Groups 
2-5 are any of them present. This ammonium radical is 
easily identified by adding a strong base, like sodium 
hydroxide, to it and heating. Its presence is shown by 
the odor of ammonia gas: or in smaller quantities by the 
fact that moist red litmus paper held in the gases escaping 
from this heated mixture turns blue. 

(6) Magnesium is identified by the precipitate of am¬ 
monium-magnesium phosphate it forms when di-sodium 
acid phosphate solution is added to the “Sixth Group.” 
The reaction is: 

Mg(N0 3 ) 2 + NH 4 OH + HNa 2 P0 4 

-> 1 NH 4 MgP0 4 + 2 NaN0 3 + H 2 0. 

(c) Sodium is identified in the “ Sixth Group ” by the char¬ 
acteristic yellow color it imparts to the Bunsen flame. 
Very few sodium compounds are insoluble: precipitation 
tests are therefore seldom used. 

(d) Potassium is identified in the “ Sixth Group” by the 
color it imparts to the Bunsen flame when that flame is 
viewed through a blue glass. This lilac color may be seen 
without the blue glass in the absence of sodium. When 
sodium is present the yellow color imparted to the flame by 
this metal is absorbed by the blue glass which allows only 
the blue rays to pass. 


120 


Qualitative Analysis. 


If a small portion of the “Sixth Group” is evaporated to 
dryness and heated until all the ammonium compounds are 
driven off and the cooled residue is dissolved in water this 
will give a characteristic yellow precipitate with chloro- 
platinic acid. The reaction is: 

2 KN0 3 + H 2 PtCl 6 -> 2 HN0 3 + I K 2 PtCl 6 . 

Care must be taken to drive off all the ammonium com¬ 
pounds before this test is made, as the ammonium radical 
produces a compound with chloro-platinic acid that is 
identical in appearance with the potassium salt. 


Group VI. 


121 


Experiment 40. 

Title: Analysis of an Unknown Solution which may 
contain any of the Metals of the Sixth Group. 

1. Directions. Follow the directions given in Experi¬ 
ment 39. 

2. The Written Record. Write the result of this analysis 
in tabular form as shown below. 


NH4. 

Mg. 

Na. 

K. 

Unknown solu- 

Portion 2. 

Portion 3. 

Portion 3. 

tion. 

+ 

Test on Pt. wire 

Test on Pt. wire 

Portion 1 

Equal vol. of 

in the Bunsen 

in Bunsen 

+ 

NH 4 C1 

flame a char¬ 

flame, a red- 

NaOH. 

+ 

acteristic. 

violet color in¬ 

Boil. 

NH 4 OH 

Yellow color. 

dicates potas¬ 

Odor of NH 3 indi¬ 

to alkaline 

Indicates sodium. 

sium. 

cates the am- 

reaction 


If sodium is 

monium radical. 

+ 


present the 

Hold moist red 

Na 2 HP0 4 . 


color is ob¬ 

litmus paper in 

White cryst. ppt. 


served 

the gas disen¬ 

is NH 4 MgP 0 4 . 


through a 

gaged from the 

and indicates 


piece of blue 

mixture. 

magnesium. 


glass. 

If the litmus 

If the NH 4 Mg- 


Evaporate to 

turns blue the 

P0 4 fails to dis¬ 


dryness. 

presence of the 

solve in warm 


Drive off any 

ammonium radi¬ 

NaOH the 


NH 4 com¬ 

cal is confirmed. 

presence of 
magnesium is 
confirmed. 


pounds. 
Dissolve resi¬ 
due in a little 
H 2 0. 

A few drops 
+ 

H 2 PtCl 6 . 

A yellow ppt. is 
K 2 PtCl 6 . 
Confirms 
potassium. 










122 


Qualitative Analysis. 


Experiment 41. 

Title: The Analysis of an Unknown Solution which may 
contain any of the Metals of Groups I-VI. 

1. Separation into Groups. Follow the directions given 
in Introduction 4. 

2. Analysis of the HC1 Group. Follow the directions 
given in Experiment 4, beginning with paragraph 2. 

3. Separation of the H 2 S Group into Parts I and II. 
Follow the directions given in Experiment 19, paragraph 3. 

4. Analysis of the H 2 S Group: Part I. Follow the direc¬ 
tions given in Experiment 11, beginning with paragraph 2. 

5. Analysis of the H 2 S Group: Part II. Follow the direc¬ 
tions given in Experiment 17, beginning with paragraph 2. 

6. Analysis of the NH 4 OH Group. Follow the directions 
given in Experiment 23, beginning with paragraph 2. 

7. Analysis of the (NH 4 ) 2 S 2 Group. Follow the direc¬ 
tions given in Experiment 30, beginning with paragraph 2. 

8. Analysis of the (NH 4 ) 2 C0 3 Group. Follow the direc¬ 
tions given in Experiment 36, beginning with paragraph 2. 

9. Analysis of the Alkali Group. Follow the directions 
given in Experiment 39. 

10. The Written Record. Write the results of this exper¬ 
iment in tabular form. Follow the outlines given in 
Experiments 5, 12, 18, 24, 31, 37 and 40. 

Note: The scheme for the separation of the metals: 
groups I-VI should be memorized at this point and a 
number of unknown mixtures analyzed from memory. 


Tests for the Acid Radicals. 


123 


TESTS FOR THE ACID RADICALS. 
INTRODUCTION 6 . 

1. Ground Covered. In the following experiments pro¬ 
vision is made for the detection of the common acid radicals. 
The list is: 


Chlorates. 

.... - (C10 3 ) 

Nitrates. 

.... - (NO,) 

Carbonates. 

.... = (CO.) 

Cyanides. 

.... - (CN) 

Sulphides. 

.... = (S) 

Sulphites. 

.... = (SO,) 


Chlorides.— (Cl) 

Sulphates.= (SO 4 ) 

Ferrocyanides. . . . - (FeC 6 N 6 ) 

Ferricyanides. = (FeC 6 N 6 ) 

Arsenates.= (As0 4 ) 

Arsenites.= (As0 3 ) 


2. Preliminary Observations. If an analysis for both the 
metallic ions and the acid radicals is to be made the former 
should be made first as its results will throw much light 
upon the nature of the acid radicals present. If the 
analysis of the metals is considered in the light of the 
following rules much time will frequently be saved as some 
of the tests for acid radicals may then be omitted. 

(a) Chlorides. If any of the metals of Group I are 
present chlorides are absent. 

(b) Sulphates and Sulphites. If Pb or Ba ions are found 
sulphates and sulphites are absent. 

(c) Sulphides. If any of the metals of Group II are 
found and the original solution is neutral or acid sulphides 
are absent. 

( 1 d ) Sulphides. If any of the metals of Group IV or Iron 
are present in neutral or alkaline solutions, sulphides are 
absent. 













124 Qualitative Analysis. 

(e) Carbonates. If any of the metals of Groups I-V are 
found present, or the solution tests acid, carbonates are 
absent. 

(/) Sulphites. If the solution is strongly acid sulphites 
are absent. 

(g) Arsenates and Arsenites. If the solution is neutral 
and any of the metals of Groups I-V are present arsenates 
and arsenites are absent. 


Tests for the Acid Radicals. 


125 


Experiment 42. 

Title: Tests for Chlorates and Nitrates. 

1. The Blowpipe Test. If the material to be tested is a 
liquid evaporate 10 c.c. of the solution to dryness over a 
low flame. Avoid too much heat or some of the acid 
radicals may be decomposed. The heating is best done in a 
small porcelain dish. Place a little of the solid residue left 
in the dish on a piece of charcoal and heat with the mouth 
blowpipe. Deflagration (rapid combustion) or decrepita¬ 
tion (flying apart of crystals) indicate chlorates or nitrates 
or both. 

2. A Test for Chlorates. Pour a drop or two of concen¬ 
trated sulphuric acid into a small watch glass and add a 
small particle of the solid from (1). The formation of a 
brown color and a characteristic “Chlorous ’’ odor indicate 
the presence of chlorates. Only small quantities of the 
substances for this test should be used and these should 
not be heated as the products formed are explosive. The 
reactions which occur in this test are as follows: 

Sulphuric acid first liberates chloric acid from the chlorate. 

2 KClOa + H 2 S0 4 -> 2 HC10 3 + K 2 SOi. 

The chloric acid then breaks down spontaneously as follows: 

3 HCIO 3 -> H 2 0 + HCIO 4 + 2 C 10 2 . 

The color and odor referred to in the test above are due to 
the chlorine dioxide, a yellow gas above 10° C. The 
explosive character of this mixture, when heated slightly, 
is due to the decomposition of the C10 2 with the liberation 
of large quantities of heat into its elements. 


126 


Qualitative Analysis. 


When odor tests are used the pupil should first make the 
experiment with the known substance and then with the 
unknown material and the results should be compared. 
In. this test for chlorates the odor is more reliable than the 
color which may be covered more or less by the presence of 
other substances. 

3. Tests for Nitrates, (a) Mix a small quantity of the 
substance under test with 5 c.c. of concentrated sulphuric 
acid in a test-tube. If the mixture becomes hot cool it by 
running cold water on the outside of the test-tube. To this 
cool mixture add an equal volume of a strong solution of 
ferrous sulphate. This should be poured slowly down the 
side of the test-tube containing the sulphuric acid while this 
tube is held in a slanting position. If this is carefully done 
the ferrous sulphate will float upon the sulphuric acid 
mixture. A brown ring formed at the junction of the two 
liquids indicates nitrates. 

The reactions involved in this test are shown by the 
following chemical equations: 

Sulphuric acid first liberates nitric acid from the nitrate 
present, thus: 

NaN0 3 + H 2 S0 4 -> NaHS0 4 + HN0 3 . 

The nitric acid thus produced oxidizes some of the ferrous 
to ferric sulphate with the production of nitrogen dioxide, 
thus: 

2 HN0 3 + 6 FeS0 4 + 3 H 2 S0 4 

-> 3 Fe 2 (S0 4 ) 3 + 4 H 2 0 + 2 NO. 

The NO then reacts with the excess of ferrous sulphate and 
forms with it the compound (FeS0 4 ) 2 .N0. The brown 


Tests for the Acid Radicals. 


127 


color of the ring is due to this compound, nitrosyl ferrous 
sulphate. 

(6) Some substances interfere somewhat with the test 
just given under (a). If there is any doubt about the result 
of the brown ring test the following test should be made. 
To five cubic centimeters of the solution to be tested add 
enough potassium hydroxide to make the mixture strongly 
alkaline. This mixture should be made in a test-tube 
provided with a one-hole stopper and U-shaped delivery 
tube. Add a piece of aluminum wire to the alkaline mix¬ 
ture and warm until a gas is evolved. Put the stopper in 
place and pass the gas through the delivery tube into 10 
c.c. of water to which a few drops of “Nessler’s Reagent” 
has been added. The formation of a yellowish-brown 
precipitate is a sure indication of nitrates. Nothing inter¬ 
feres with this test. The test is explained as follows: 
The nitric acid is first reduced by the KOH and A1 to 
ammonia. Thus: 

3 HN0 3 + 8 A1 + 8 KOH + A -> 3 NH 3 + 8 KA10 2 + H 2 0. 

The ammonia gas then reacts with the Nessler’s reagent as 
follows: 

NH 4 OH + 2 K 2 HgI 4 + 3 KOH -> NHg 2 I + 7 KI + 4 H 2 0. 

The mixture of potassium hydroxide and potassium mer¬ 
curic iodide, K 2 HgI 4 , is Nessler’s reagent. The yellowish- 
brown precipitate is dimercur-ammonium iodide, NHg 2 I. 


128 


Qualitative Analysis. 


Experiment 43. 

Title: Preliminary tests for Sulphides, Sulphites, Cy¬ 
anides and Carbonates. 

1. Preparation of the Test Material. If the substance to 
be tested is in the form of a solution, evaporate 10 c.c. of 
it in a porcelain dish to dryness. Use a low flame and be 
careful not to overheat the dry material left as a residue or 
the acid radicals may be decomposed. If any of the 
material from the previous experiment remains this may of 
course be used and the step just outlined saved. 

Prepare some dilute hydrochloric acid (1-3). This must 
be entirely free from any odor. If necessary make the 
acid still more dilute. Reserve these prepared materials 
for the following tests. 

2. Sulphides. Put a small amount of the solid residue 
prepared above in a test-tube and add 1 c.c. of the odorless 
hydrochloric acid. If no gas is disingaged warm the con¬ 
tents of the tube. If there is still no effervescence sulphides, 
sulphites, cyanides and carbonates are absent and the 
following tests in this experiment may be omitted. 

If a gas is disingaged carefully note its odor. If it has 
the odor of rotten eggs sulphuretted hydrogen is present in 
the gas and the presence of sulphides is proved. Dilute 
hydrochloric acid disingages sulphuretted hydrogen from 
all sulphides. The equation for this reaction is: 

FeS + 2 HC1 -> FeCl 2 + H 2 S. 

Hold a piece of filter paper moistened with lead acetate 
solution in the escaping gas. If sulphuretted hydrogen is 
present in the gas the paper will turn a brown-black color. 
In this case the presence of sulphides is confirmed. 


Tests for the Acid Radicals. 


129 


3. Sulphites. In a similar manner if when hydrochloric 
acid is added to a little of the solid under test and a gas is 
disingaged the gas has the odor of burning sulphur (sulphur 
dioxide) then sulphites are present. The chemical equa¬ 
tion for this reaction is: 

Na 2 S0 3 + 2 HC1 -> 2 NaCl + H 2 0 + S0 2 . 

Hydrochloric acid liberates sulphur dioxide from all sul¬ 
phites. 

Hold moist litmus paper (blue) in the escaping gas. If 
this paper is first turned red and then decolorized, the 
presence of sulphites is confirmed. 

4. Cyanides. If the gas liberated by the action of 
hydrochloric acid has the odor of bitter almonds, cyanides 
are present. Avoid inhaling this gas in quantity greater 
than the small amount necessary to detect its odor. The 
gas is hydrocyanic acid, a violent poison. The equation 
for the production of this gas is: 

KCN + HC1 -» KC1 + HCN. 

If sulphides or sulphites are present with the cyanides the 
odor of the hydrocyanic acid will probably be covered by 
the stronger odors of sulphuretted hydrogen and sulphur 
dioxide. In this case the following confirmatory test should 
be made. 

To a little of the solid in an evaporating dish add a drop 
or two of yeDow ammonium sulphide. Heat over a water 
bath until the ammonium sulphide is colorless. Acidify 
with very dilute hydrochloric acid (H 2 S must not be dis¬ 
ingaged) and then add a drop of a solution of ferric chloride. 
The formation of a blood-red solution of ferric sulpho- 


130 


Qualitative Analysis. 


cyanide confirms the presence of cyanides. The equations 
for the reactions of this test are: 

4 KCN + 2 (NH 4 ) 2 S 4 -> 4 NH 4 CNS + 2 K 2 S + S 2 . 
FeCl 3 + 3 NH 4 CNS -> 3 NH 4 C1 + Fe(CNS) 3 . 
Fe(CNS) 3 is the red color. 

5. Carbonates. If the gas evolved when dilute hydro¬ 
chloric acid is added to the solid under test is odorless it is 
carbon dioxide and indicates carbonates. 

To confirm the presence of carbonates pour 2 c.c. of 
perfectly clear limewater into a test-tube and pour a little 
of the gas just generated into this test-tube. Pour the 
heavy carbon dioxide gas only: do not allow any of the 
liquid to pass into the limewater. Shake the tube con¬ 
taining the limewater and the added gas. If a precipitate 
is formed (white) or the liquid looks turbid it is due to the 
formation of calcium carbonate. In this case the presence 
of carbonates is confirmed. This test will identify carbon¬ 
ates in the presence of sulphides, sulphites, and cyanides. 
The chemical reactions for this test are: 

Ca(OH) 2 + C0 2 -> CaC0 3 1 + H 2 0. 

For the generation of the carbon dioxide gas from the test 
substance the equation is: 

Na 2 C0 3 + 2 HC1 -> 2 NaCl + H 2 0 + C0 2 . 

If the amount of carbonate is very small the turbidity 
produced will be slight. In this case compare the test 
limewater with a fresh sample of the limewater taken from 
the supply. The difference in clearness of the two fluids 
is easily detected. 


Tests for the Acid Radicals. 


131 


Experiment 44. 

Title: Tests for Ferricyanides, Ferrocyanides, Sulphates, 
Sulphites and Chlorides. 

1. Preparation of the Solution. Pour 20 c.c. of the un¬ 
known solution into a beaker and add enough solid sodium 
carbonate to make the mixture strongly alkaline to litmus. 
Boil the contents of the beaker slowly for five minutes and 
filter the solution hot. If an appreciable quantity of the 
liquid boils away this should be made up with water before 
filtering. The object of this treatment with sodium car¬ 
bonate is to precipitate out the metallic ions of the first five 
groups of metals and leave the acid radicals in the filtrate 
largely as salts of sodium. 

Discard the precipitate and reserve the clear filtrate for 
the following tests. 

2. A Preliminary Test. To 3 or 4 c.c. of the filtrate 
reserved above add dilute nitric acid to acid reaction (litmus 
test). To this add a few drops of silver nitrate solution. 
If a precipitate forms upon the addition of the silver nitrate 
it shows that some or all of the following acid radicals are 
present: Chlorides, Cyanides, Ferricyanides, Ferrocyanides.' 
If no precipitate is formed upon the addition of the silver 
nitrate it shows that these acid radicals are absent and no 
further tests for them need be made. 

If upon adding the nitric acid in the test just described a 
yellow precipitate forms before the silver nitrate is added 
it is arsenic sulphide and indicates the presence of both 
Sulphides and Arsenites. In the event of this yellow pre¬ 
cipitate forming, it should be filtered off and discarded 
before the silver nitrate is added. This test serves as a 
check upon the result of the last and the following experi¬ 
ment. 


132 


Qualitative Analysis. 


If in the previous experiment there was any doubt about 
the presence of sulphides, and this yellow precipitate does 
not form when the nitric acid is added, a drop or two of a 
solution of sodium arsenite may be added: if sulphides are 
present the precipitate of arsenic sulphide will at once form. 

3. The Test for Ferricyanides. To three or four c.c. of 
the prepared solution reserved from (1) add dilute hydro¬ 
chloric acid to acid reaction (litmus test) and then an equal 
volume of ferrous sulphate solution. The formation of a 
blue precipitate (Turnbull's blue) indicates the presence of 
ferricyanides. The equation for this reaction is: 

2 Na3FeC6N 6 -j- 3 FeS04 —> 3 Na2S04 -|- Fe 3 (FeCeN6)2* 

4. The Test for Ferrocyanides. To three or four c.c. of 
the prepared solution reserved from (1) add dilute hydro¬ 
chloric acid to acid reaction and then an equal volume of a 
solution of ferric chloride. The formation of a blue pre¬ 
cipitate (Prussian blue) indicates ferrocyanides. The chemi¬ 
cal equation for this reaction is: 

3 Na 4 Fe(C 6 N 6 ) + 4 FeCl 3 -> 12 NaCl + Fe 4 (FeC 6 N 6 ) 3 . 

5. The Tests for Sulphites and Sulphates. To 3 or 4 c.c. 

of the prepared solution reserved from (1) add a few drops 
of a solution of barium chloride. If a white precipitate 
forms add dilute hydrochloric acid in excess and boil. If 
the precipitate dissolves in the hot acid the presence of 
sulphites is shown. If the white precipitate fails to dissolve 
in the hot acid then sulphates are present. 

The chemical reactions for these tests are: 


Na 2 S0 3 + BaCl 2 -» 2 NaCl + BaS0 3 .1 


Tests for the Acid Radicals. 


133 


BaS0 3 + 2 HC1 -» BaCl 2 + H 2 0 + S0 2 . 

Na 2 S0 4 + BaCl 2 -> 2 NaCl + BaS0 4 . 1 

6. The Test for Chlorides. To the balance of the pre¬ 
pared solution reserved from (1) add nitric acid (dilute) to 
acid reaction (litmus test). If the yellow precipitate of 
arsenic sulphide, referred to above, forms, filter it off. To 
the clear filtrate add a few drops of silver nitrate. If a 
white precipitate forms, and cyanides, ferrocyanides and 
ferricyanides are absent, then this white precipitate is 
silver chloride and indicates the presence of chlorides. 
Allow the precipitate to settle and pour off most of the 
liquid. To the precipitate add dilute ammonium hydroxide 
in excess. If the white precipitate dissolves in the am¬ 
monium hydroxide the presence of chlorides is confirmed. 
The equations for these reactions are: 

NaCl + Ag(N0 3 ) -> NaN0 3 + | AgCl. 

AgCl + 2 NH 4 OH -> Ag(NH 3 ) 2 C1 + 2 H 2 0. 

If, however, cyanides, ferricyanides or ferrocyanides have 
been found in the solution then the precipitate is not neces¬ 
sarily silver chloride and a further confirmatory test must be 
made. 

Reprecipitate the silver chloride from its solution in 
ammonium hydroxide by adding to it an excess of dilute 
nitric acid. Allow this precipitate to settle and then 
decant off most of the fluid. Pour the remaining fluid and 
the precipitate into a small porcelain crucible. Heat this 
gently until all the liquid is boiled away and then strongly 
(red heat). This will destroy cyanides, ferricyanides and 
ferrocyanides but will leave the silver chloride, if it is 
10 


134 


Qualitative Analysis. 


present. Cool the crucible and then add a little dilute 
sulphuric acid and a small piece of zinc. Let a brisk effer¬ 
vescence continue for 3 minutes and then filter the liquid 
in the crucible into a test-tube. To this add a little dilute 
nitric acid and then a few drops of silver nitrate. The 
formation of a white precipitate of silver chloride, soluble 
in ammonium hydroxide, indicates chlorides. 

The reaction which takes between the zinc, the sulphuric 
acid and the silver chloride is as follows: 

2 AgCl + H 2 SO 4 -f- Zn —» ZnCL T* Ag 2 S 04 + 2H. 

It is the zinc chloride which gives the test for chlorides. 


Tests for the Acid Radicals. 


135 


Experiment 45. 

Title: Tests for Arsenites and Arsenates. 

1. Preparation of the Solution. Prepare 10 c.c. of the 
unknown solution by boiling it with an excess of sodium 
carbonate to remove the metallic ions. Filter off any pre¬ 
cipitate formed, and discard it. Reserve the clear filtrate 
for the following tests. 

2. Tests for Arsenites. To one third of the filtrate pre¬ 
pared in (1) add dilute nitric acid in slight excess. If a 
yellow precipitate forms it is arsenic sulphide and indicates 
the presence of arsenites. If no precipitate forms upon the 
addition of the HN0 3 pass sulphuretted hydrogen gas 
through the mixture for 10 seconds. If a yellow precipi¬ 
tates forms it is arsenic sulphide and shows the presence of 
arsenites. The chemical equation for this reaction is: 

2 Na 3 As0 3 4~ 3 H 2 S 4- 6 HN0 3 

—> 6 NaN0 3 -j- As 2 S 3 4* 0 H 2 O* 

Arsenates do not react with H 2 S unless the solution is 
diluted, warmed and the gas passed for a long time. 

3. Tests for Arsenates. To one third of the solution 
prepared in (1) add dilute nitric acid to slight excess and 
then silver nitrate solution to complete precipitation. 
Allow this precipitate to settle and then decant off the clear 
liquid. Discard the precipitate. To the clear fluid add 
an equal volume of ammonium molybdate solution and 
warm the mixture. The formation of a finely divided 
yellow precipitate indicates arsenates. Arsenites do not 
give this test. 


APPENDIX I. 

The Set of Apparatus Needed for Each 
Student’s Locker. 

APPENDIX II. 

Complete List of Chemical Reagents Needed 
for this Book. 

Note: Only the important dilute acids and the bases need 
be supplied to each student individually. The other 
reagents may be kept on a shelf at some convenient point 
in the laboratory and may be used by all students when 
needed. 


APPENDIX III. 

Solids Needed for the Preparation of the Solutions 
for Analysis. 


Appendix I. 


137 


APPENDIX I. 

THE SET OF APPARATUS NEEDED FOR EACH 
STUDENT’S LOCKER. 

6 Test-tubes 6" x §". 

2 Cone Flasks 250 c.c. 

1 Glass Funnel 2|" (diameter): long stem. 

2 Glass Beakers 125 c.c.: Griffin form. 

1 Watch Crystal 2" in diameter. 

*1 Piece of Blue Glass 2 x 3". 

1 Glass Stirring Rod 6" long. 

1 Piece of Glass Tubing 6" long (J" in diameter). 

1 Porcelain Evaporating Dish 3|" in diameter. 

*1 Porcelain Crucible If" in diameter. 

1 Package of Filter Paper " in diameter. 

1 Package of Filter Paper 3" in diameter. 

1 Tube of Blue Litmus Paper (in strips). 

1 Tube of Red Litmus Paper (in strips). 

*1 Platinum Wire mounted in glass handle 4" long. 

*1 Platinum Foil 1" Square. 

1 Test-tube Rack. 

1 Test-tube Holder. 

1 Test-tube Brush. 

1 Ringstand: two rings and one clamp. 

1 Bunsen Burner. Two feet of rubber hose to fit. 

*1 Small Triangular File. 

1 Pair of Tweezers or Crucible Tongs. 

1 Wire Gauze 5" square. 

* Note .—Articles marked * are not used very frequently. These 
may be purchased in smaller quantity and loaned to pupils when 
required if it is desired to keep the equipment expense down. 


138 Qualitative Analysis. 

1 Two-hole Rubber Stopper to fit Flask with wash bottle 
tubes. 

*1 Pipe Stem Triangle to fit porcelain crucible. 

*1 Small Water Bath. 

*1 Mouth Blowpipe. 

*1 Stick of Charcoal. 


Appendix II. 


139 


APPENDIX II. 

COMPLETE LIST OF CHEMICAL REAGENTS REQUIRED 
FOR THIS BOOK. 

Acids: Acetic, CH 3 COOH, U.S.P. 

*Chloroplatinic, Ii 2 PtCl 6 . 

Hydrochloric, HC1, cone. 

Hydrochloric, HC1, dilute (1-3). 

Nitric, HNO3, cone. 

Nitric, HN0 3 , dilute (1-3). 

Sulphuric, H 2 S0 4 , cone. 

Sulphuric, H 2 S0 4 , dilute (1-10). 

Alcohol: Ethyl, C 2 H 5 OH, 95 per cent. 

Aluminum Wire (in short pieces). 

Ammonium Acetate, CH 3 COONH 4 , 5 per cent. 
Ammonium Carbonate, (NH 4 ) 2 C0 3 , 5 per cent. 
Ammonium Chloride, NH 4 C1, 20 per cent. 

* Ammonium Molybdate, (NH 4 ) 2 Mo 7 0 24 . 

Ammonium Oxalate, (COO) 2 . (NH 4 ) 2 , 5 per cent. 
Ammonium Sulphate, (NH 4 ) 2 S0 4 , 10 per cent. 
Ammonium Sulphide, (NH 4 ) 2 S 2 (yellow) (1-3). 

Bases: Ammonium Hydroxide, NH 4 OH, cone. 

Ammonium Hydroxide, NH 4 OH, dilute (1-3). 
Calcium Hydroxide, Ca(OH) 2 , limewater, satur¬ 
ated. 

Potassium Hydroxide, KOH, 10 per cent. 

Sodium Hydroxide, NaOH, 10 per cent. 
Dimethylglyoxime, [(CH 3 )C : N.OH] 2 , 1 per cent in ethyl 
alcohol. 

* Ferrous Sulphate, FeS0 4 , 5 per cent. 

Iron Nails, Fe (small). 

*Nessler , s Solution. 


140 


Qualitative Analysis. 


Potassium Chromate, K 2 Cr0 4 , 5 per cent. 

Potassium Chlorate, KC10 3 (solid). 

Potassium Cyanide, KCN, 5 per cent. CAUTION. 

Potassium Sulphocyanide, KCNS, 5 per cent. 

Sodium Arsenite, Na 3 As0 3 , 5 per cent. 

Sodium Carbonate, Na 2 C0 3 , 5 per cent. 

Sodium Carbonate, Na 2 C0 3 (solid). 

Sodium Phosphate, Na 2 HP0 4 , 5 per cent. 

Sodium Tetraborate, Na 2 B 4 0 7 (borax) (solid). 

Sulphuretted Hydrogen Gas, H 2 S, from Kipp generator. 
*Stannous Chloride, SnCl 2 . 

Silver Nitrate, AgN0 3 , 5 per cent. 

Tartaric Acid, (CHOH) 2 . (COOH) 2 , 5 per cent. 

Zinc, Zn, metal (solid). 

Chloroplatinic Acid. Short pieces of platinum which will 
break off from time to time should be saved and dissolved 
in a little warm Aqua Regia (1 HN0 3 + 3 HC1 : by 
volume). The solution is chloroplatinic acid. 

Ammonium Molybdate Solution. Dissolve 15 grams of 
(NH 4 ) 2 Mo 7 0 24 .4 H 2 0 in water and make up to 100 c.c. 
Add this solution of ammonium molybdate to 100 c.c. of 
nitric acid of sp. gr. 1.2 (1 HN0 3 cone. + 1 H 2 0 by volume) 
slowly. If to this mixture 30 grams of ammonium nitrate 
is added the sensitiveness of the reagent will be considerably 
increased. 

Calcium Hydroxide Solution: Limewater. Place a hand¬ 
ful or two of slaked lime, Ca(OH) 2 , in a large acid bottle 
and fill the bottle with water. Shake well and then allow 

* Note .—Directions for the preparation of the reagents marked * are 
given below. Where the reagent is followed by a per cent its solution 
in water of that strength is indicated. These solutions need be only 
approximate. 


Appendix II. 


141 


the mixture to stand indefinitely. The clear liquid de¬ 
canted off as required will be a saturated solution of lime- 
water. 

Nessler’s Solution, (a) Dissolve 8 grams of HgCl 2 in 
250 c.c. of H 2 0. (6) Dissolve 17 grams of KI in 100 c.c. 

of H 2 0. Add (a) to (6) until a slight permanent precipitate 
forms. Add 80 grams of solid KOH to this mixture. Cool. 
Then add more of (a) to the mixture a little at a time until a 
slight permanent precipitate forms. Allow this precipitate 
to settle. Decant off the clear solution. This is Nessler’s 
reagent. It is advisable to make this reagent up in quantity 
and keep it as the old Nessler’s is more sensitive than it is 
when freshly prepared. 

Stannous Chloride Solution. Dissolve 5 grams of stan¬ 
nous chloride in 100 c.c. of water to which a little powdered 
tin metal has been added and enough HC1 to evolve hydro¬ 
gen. Heat this mixture until the SnCl 2 is dissolved. Filter 
hot into a bottle in which a little mossy tin metal is kept. 
The hydrogen and the tin prevent the oxidation of the 
stannous chloride to stannic chloride. 


142 


Qualitative Analysis. 


APPENDIX III. 

SOLIDS NEEDED FOR THE PREPARATION OF THE 


Group I. 

SOLUTIONS FOR ANALYSIS. 

Silver Nitrate, AgN0 3 . 

Group II. 

Mercurous Nitrate, HgN0 3 . 

Lead Nitrate, Pb(N0 3 ) 2 . 

Mercuric Nitrate, Hg(N0 3 ) 2 . 

Copper Nitrate, Cu(N0 3 ) 2 . 

Bismuth Nitrate, Bi(N0 3 ) 3 . 

Cadmium Nitrate, Cd(N0 3 ) 2 . 

Sodium Arsenite, Na 3 As0 3 . 

Antimony Chloride, SbCl 3 . 


Stannous Chloride, SnCl 2 . 
Group III. Ferrous Nitrate, Fe(N0 3 ) 2 . 


Group IV. 

Aluminum Nitrate, A1(N0 3 ) 3 . 

Chromium Nitrate, Cr(N0 3 ) 3 . 

Cobalt Nitrate, Co(N0 3 ) 2 . 

Nickel Nitrate, Ni(N0 3 ) 2 . 

Group V. 

Manganese Nitrate, Mn(N0 3 ) 2 . 

Zinc Nitrate, Zn(N0 3 ) 2 . 

Barium Nitrate, Ba(N0 3 ) 2 . 

Group VI. 

Strontium Nitrate, Sr(N0 3 ) 2 . 

Calcium Nitrate, Ca(N0 3 ) 2 . 

Magnesium Nitrate, Mg(N0 3 ) 2 . 

Sodium Nitrate, NaN0 3 . 

Potassium Nitrate, KN0 3 . 


Ammonium Nitrate, NH 4 N0 3 . 

The Acid Radicals. Potassium Chlorate, KC10 3 . 

Sodium Nitrate, NaN0 3 . 
Potassium Cyanide, KCN. 
Sodium Sulphide, Na 2 S. 


Appendix III. 


143 


The Acid Radicals. Sodium Sulphite, Na 2 S0 3 . 

Sodium Carbonate, Na 2 C0 3 . 
Sodium Chloride, NaCl. 

Sodium Sulphate, Na 2 S0 4 . 
Potassium Ferricyanide, K 3 FeC 6 N 6 . 
Potassium Ferrocyanide, K 4 FeC 6 N 6 . 
Sodium Arsenite, Na 3 As0 3 . 

Sodium Arsenate, Na 3 As0 4 . 


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